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High School/JEE/NEET/IPhO Physics | 17-19 Yrs

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  1.  
  2. can i see these lectures with basic knowledge of newtons laws of motion as it is my backlog?My respected sir,am waiting dearly for answer ??
    2 years ago by

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  3.  
  4. when can i get the solution of the set one questions?
    2 years ago by

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  5.  
  6. how to increase speed of video on this app?
    2 years ago by vedant bande

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  7.  
  8. sir is energy conservation a special case of we theorem when there is no loss due to external force
    2 years ago by likun mohapatra

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  9.  
  10. sir is neet 2021 syllabus reduced? if so is it from class 12 cbse board syllabus or class 11 and 12 cbse board syllabus?pls help
    3 years ago by

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  11.  
  12. unable to understand this question sir
    3 years ago by Rahul Kumar

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  13.  
  14. Sir why you have taken final elongation as maximum elongation?
    3 years ago by Indra Jain

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  15.  
  16. Respected sir, i am not able to find the relation of v1 and v2 . It would be great help if you will explain how you have related v1 and v2
    3 years ago by

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  17.  
  18. Respected sir, I have doubt that how v1cos theta= v , it should be v1 tan theta = v
    3 years ago by

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  19.  
  20. Respected sir, I have doubt that how v1cos theta= v , it should be v1 tan theta = v
    3 years ago by

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  21.  
  22. Respected sir, I have doubt that how v1 cos theta = v , it should be v1 tan theta = v
    3 years ago by

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  23.  
  24. So one basis of above statement can we say that energy can never be created nor be destroyed?? as there is always a negative work is done when there is positive work!!
    3 years ago by arnav raj

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  25.  
  26. Sir if we have a long chain , part of which is on a L meter high platform and the rest part is on the ground and there is a part of the chain which is vertical ( between the position where the platform ends and t ground starts). Then if I slowly pull the chain, how much work is required to pull it by X meters? sir plz tell me the approach and solution, I'm not able to write the equations.
    4 years ago by NightcoRohak

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  27.  
  28. is this is possible that sum of forces is zero and even after that body is not in equilbrium
    4 years ago by Jasper Bhardwaj

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  29.  
  30. why work done by spring with elongation y is taken negative and it is in the direction of motion of block B
    4 years ago by editor jst

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  31.  
  32. Where is the collison concept?
    5 years ago by neeraj chatterjee
    Ans 1 ->
    in system of particles
    5 years ago by RAHUL VERMA

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  33.  
  34. where sir zero work?
    5 years ago by Arun Prasath
    Ans 1 ->
    if there is no component of resultant displacement in the direction of force or if the angle between force and displacement is 90 or if the angle between force and velocity is 90 then work done in all these cases is zero .
    5 years ago by t arjun

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  35.  
  36. Sir, Why work done by tension has not been considered?
    5 years ago by Adarsh Mall

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  37.  
  38. Sir, if ve work means supply of energy, then why is the potential energy decreased?
    5 years ago by Adarsh Mall

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  39.  
  40. in module 12 of work energy...if we take minus the answer is 3
    5 years ago by Saurav Tiwari

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  41.  
  42. sir in modulo 12 of work energy....you have written Wpr=Ur--Up=7 sir it should be plus
    5 years ago by Saurav Tiwari

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  43.  
  44. Sir in your last illustration why did you not take work done by forces in direction of displacement i mean when the block hits the spring it must exert some force on it right so work should be done but you have not accounted that in the equation?
    5 years ago by Madhav Sharma

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  45.  
  46. Why are we taking that 'y' is the maximum elongation of the block ? What I mean is that the force needed to break the lower block from the ground can be achieved before the spring reaches it's maximum elongation , right ?
    5 years ago by Bidisha Maitra

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  47.  
  48. An electron moves in a straight line towards east with a constant speed of 8× 10^7 m/s. It has electric, magnetic and gravitatinal forces acting on it. Find the total work if displacement is 1m.
    5 years ago by Diwa Pankaj

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  49.  
  50. sir if a is moving by dl, why (lambda)*dx is taken as mass?? why mass is not (lambda)*dl ????
    5 years ago by Dharamjeet Singh

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  51.  
  52. how the displacement of block B is root5-1
    5 years ago by Mucchad Pie

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  53.  
  54. Sir why did we use the modulus of dU/dx , shouldn't we use it with negative sign? wherein we finally get acceleration as -16 m/s^2
    5 years ago by Zulfiqar Ravzatul Hussain

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  55.  
  56. give an example of conservative feild
    5 years ago by Jeet Shah
    Ans 1 ->
    Electric field is an example of conservative field
    5 years ago by Zulfiqar Ravzatul Hussain

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  57.  
  58. sir how do came to know that external agent is doing work and not conservative field itself??
    5 years ago by Divit Goyal

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  59.  
  60. EMF is the work done Per unit charge What will be the nature of the force responsible for this work done - conservative or nonconservative
    5 years ago by nikhil gupta

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  61.  
  62. VGood teaching sir All concept my clear
    5 years ago by Aditya Pathak

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  63.  
  64. Thanks a lot sir Vvvvv thanks
    5 years ago by Aditya Pathak

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  65.  
  66. Sir, I used force method to solve this question. F-kx=#m2g kx=#m1g So, F=#(m1 m2)g Sir, can you please tell me what have I missed? Thank you. PS:-I have used # for mu.
    6 years ago by Ayushi Jain

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  67.  
  68. Why is dl=2dx ?
    6 years ago by Dhruv Malhotra

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  69.  
  70. Is it necessary that non conservative forces always dessipates energy
    6 years ago by mahesh Hingankar

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  71.  
  72. I did not understand a bit about positive and negative work or gaining and supplying energy.
    6 years ago by HARSHA DARBHASAYANAM
    Ans 1 ->
    work done is positive when something is displaced along the force .it is negative when displacement is opposite to the direction of force .eg : - when a ball is projected upwards work done by gravity is negative [as gravitational force acts downwards and the ball is going upward therefore displacement and force are opposite in direction] and it is positive when the ball moves downward [as gravitational force acts downwards and the ball is going downward therefore displacement and force are same in direction] . hope my answer helps . best regards .
    5 years ago by t arjun

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  73.  
  74. Why you took distance as vt1 and vt2??there is retardation also.
    6 years ago by Sandal Agarwal

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  75.  
  76. Not getting why it will bounce off (x y) I mean initial compression was x and final was y. Now as it bounce off x but some energy is consumed for compression of spring (y) so net bouncing off distance should be (x-y) not (x y)??
    6 years ago by Sandal Agarwal

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  77.  
  78. A Force of 20N compresses a spring with a constant 50 N/m.How much energy is stored in the spring?
    6 years ago by Prajeii

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  79.  
  80. sir please provide me with the explanation of q 11 of the que set 1
    6 years ago by
    Ans 1 ->
    try it after doing indefinite integration chap proprly
    6 years ago by shreyash

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  81.  
  82. Spring always applies its restoring force in the direction of its natural lenght when it is deformed. Is this right?
    6 years ago by

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  83.  
  84. Superb now Now my concepts are clear
    6 years ago by Sarju Panchal

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  85.  
  86. sir i cant find the illustration in the shm section..... please attach the link
    6 years ago by Aayush Srivastava

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  87.  
  88. sir i hve a sum doubt can i ask u plz
    6 years ago by nallabothu shashank

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  89.  
  90. Q- The kinetic energy of projectile at its highest position is K. If the range of projectile is four times the height of projectile , then the initial kinetic energy of the projectile is?
    6 years ago by srishti gautam

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  91.  
  92. sir , my question is Q-a pump is required to lift 800 kg of water per minute from a 10m deep well and eject it with a speed of 20m/s . Find power in watts of the pump ?
    6 years ago by srishti gautam

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  93.  
  94. How is negative work done with the elongation of the spring?
    6 years ago by Aarohi Khodkumbhe

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  95.  
  96. Around 6:56, Sir talked about the field forces or the conservative forces of the system. which are those field forces in this particular example?
    6 years ago by Aarohi Khodkumbhe

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  97.  
  98. Sir why didn't you consider air resistance? Please answer.
    6 years ago by Aladdin

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  99.  
  100. i just drawn fbd and balanced the forces what is my mistake
    7 years ago by Sanskar Bhargava

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  101.  
  102. I took speed of block at the instant it hit the pan i.e. u = root(2gh) as K.E. Initial and final K.E. as 0 and x came out to be root(2mgh/k). What did i do wrong?
    7 years ago by Udit Gupta

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  103.  
  104. we should assume the mass of boy equal to that of block in this case for them to be displaced equally in opposite directions?
    7 years ago by Sarthak Kapil

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  105.  
  106. what about kinetiic energy of washer wwhen it hets to support lower B
    7 years ago by Ram niwash

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  107.  
  108. sir when a boy is applying a force f on block (as explained in lecture) we studied an equal but opposite force acts on boy as well. but this force is not causing the boy to move..so how come is the block doing work?why isnt it 0 sir?
    7 years ago by Ajay Vashishtha
    Ans 1 ->
    theres no friction between him and floor..and i think his mass must be equal to the blocks mass
    7 years ago by Sarthak Kapil
    Ans 2 ->
    Yes my friend you are right but When the boy is applying force on the block the block is also applying same amount of force on the boy in opposite directions and the forces where cancel Each Other, till the force applied by the boy is less than limiting friction and if the force is exceeded limiting friction then a block will tend to move the direction of force
    5 years ago by Adarsh mishra

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  109.  
  110. Sir How to justify that work done is equal to the product of force and displacement?
    7 years ago by Eswar Prem
    Ans 1 ->
    w=f.s f=ma s is displacement and work is something which we did so therefore when we pull a mass some accelaration is produced which will lead us to cover a distance integerating all this we will get work done is equall to the dot product of force and displacement
    7 years ago by Mohseen Chawhan

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  111.  
  112. a block hangs freely from the end of spring.a boy then slowly pushes the block upwards so that the spring becomes strain free. the gain in gravitational potential energy of the block during the process is equal to : (a) the work done by boy against the gravitational force acting on the block (b) the loss of energy stored in the spring (c) the work done by the block plus the loss of energy stored in the spring (d) the work done on the block by the boy minus the the work done by tension in spring plus the loss of energy stored in the spring.
    7 years ago by madhvan gupta
    Ans 1 ->
    When the block is being displaced upward by h then boy is doing +ve work as well as spring is also doing positive work and work done by gravity is -ve so here work done by boy plus the work done by spring will be the gain in gravitational potential energy of the block...
    7 years ago by Physics Galaxy
    Ans 2 ->
    When the block is being displaced upward by h then boy is doing +ve work as well as spring is also doing positive work and work done by gravity is -ve so here work done by boy plus the work done by spring will be the gain in gravitational potential energy of the block...
    7 years ago by Physics Galaxy

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  113.  
  114. Do we have a proof for the expression for finding the force in the 3-d conservative space without using any complex maths?
    7 years ago by Akshunn Trivedi
    Ans 1 ->
    Proof is simple, its work energy theorem only... carefully apply work energy theorem for a particle displacing in a 3D space and then resolve its displacement along the three axes, you will get it easily...
    7 years ago by Physics Galaxy

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  115.  
  116. Sir initially only half part of the rope is hanging then why you took external force as mg I can't get that.pl explain me
    7 years ago by ansuman dixit
    Ans 1 ->
    half hanging on both sides of nail and we need to write equation for full rope...
    7 years ago by Physics Galaxy

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  117.  
  118. So sir how to visualise the cross product of DEL operator mean what does it signify?
    7 years ago by Naman Gupta
    Ans 1 ->
    DEL is the partial derivative operator given as DEL= (partial derivative wrt x)i^ + (partial derivative wrt y)j^ + (partial derivative wrt z)k^
    7 years ago by Physics Galaxy

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  119.  
  120. Sir, but what is the logic behind doing the cross product.....? How to visualise the thing that is being done by following the method?
    7 years ago by Naman Gupta
    Ans 1 ->
    cross product is defined to device a mechanism in favor of vector physical quantities when appear in product form and represent some other vector quantity then cross product is used in defining the product including the angle between these...
    7 years ago by Physics Galaxy

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  121.  
  122. Sir I wanted to know how should we identify whether a force will be conservative or non conservative? Someone told me about the curl of force =0, but I don't think that you have discussed it in your video lectures. Please reply soon Thank you for your effort
    7 years ago by Naman Gupta
    Ans 1 ->
    Direct method is what you have written i.e. curl of a Force vector if coming out to be zero then it is conservative otherwise not... but Curl is not in scope of high school physics or any competition thats why I have not covered it... that I am going to take up in advance lectures for college level physics... For your understanding you can use curl is simply cross product of DEL operator(which you use for gradient of potential energy / inverted triangle) with F vector...
    7 years ago by Physics Galaxy

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  123.  
  124. Consider a plank kept on a smooth surface and a man standing on the plank. Friction is present between man and plank. I consider the plank and man as my system. External forces acting on the system are gravitational force(conservative in nature) and the normal to the plank which is incapable of changing the energy of the system. The initial energy of the system when the man just stands on the plank is Potential energy of man + Potential energy of plank. Now the man decides to jump vertically upwards(i.e. increases his height w.r.t. reference line for potential measurement) on the plank itself. The total energy when he is moving upwards is kinetic energy of the man + Potential energy of man + Potential energy of plank. How is there an increase in the energy of the system??
    7 years ago by arpit gupta
    Ans 1 ->
    It is because to jump vertically up, man has to first bend down slightly and then push his own center of mass upward due to which his biological energy is doing work by forces inside the body and due to this work overall energy increases...
    7 years ago by Physics Galaxy

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  125.  
  126. Can a more detailed video on conservative and non-conservative forces be uploaded. It would be of great help.
    7 years ago by Abhranil Chandra
    Ans 1 ->
    For more detailed understanding you need to follow the fundamental classes on PG livestream in the topic of work and energy....
    7 years ago by Physics Galaxy

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  127.  
  128. sir in the advance illustration 12 ,you specified that simple harmonic motion concept can be used .but i am not getting the answer .i dont know where i am going wrong. please explain . hoping your soon response...
    7 years ago by ariya
    Ans 1 ->
    goto SHM topic I have solved this same problem using concept of SHM also that is much easier... If you push the upper block down by some distance from equilibrium position then this will be the amplitude of SHM and twice this distance above will be the upper extreme position where you can consider lower mass breaks off... you get the same result directly...
    7 years ago by Physics Galaxy

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  129.  
  130. I didn't understand why and how you used dL/dH for max horizontal range?? plz reply sir rishabhshrff212@gmail.com
    7 years ago by Rishabh Sharaff

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  131.  
  132. sir why did you take work done on friction as Mmg(x+y)
    7 years ago by saikiran
    Ans 1 ->
    Its force of the friction is mumg and we applied W/EE theorem between initial compression point and final extension that is x+yy.now multiplying both force and distance u will get ur answer.OK
    7 years ago by ansuman dixit

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  133.  
  134. not able to submit answer in quset please correct the error in your site as fast as possible .
    7 years ago by shivam sharma

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  135.  
  136. why final kinetic energy is zero.if constant force is applied m1 will gain some velocity.
    8 years ago by manasibandhaokar23@yahoo.com
    Ans 1 ->
    Hey yaar manasi u didnot consider friction which oppose the external force
    7 years ago by ansuman dixit

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  137.  
  138. Why did we find second derivative and why is it stable the value is positive???
    8 years ago by Ramesh Agrawal

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  139.  
  140. Sir frictional force have generally -ve work done and -ve work means gaining of energy how frictional force can gain energy
    8 years ago by Shivam pandey
    Ans 1 ->
    -ve work implies that the agent applying force must be gaining some energy. Not the force. In the case of friction. It is applied by the ground and ground gains energy in the form of dissipation energy. Hope it helped you. Thanks!
    8 years ago by Abdullah Jafar
    Ans 2 ->
    ACTUALLY THATS NOT THE REASEN WHEN A FRICTIONAL FORCE IS APPLIED SOME ENERGY IS CONSUMED BY IT AND REMAING WILL BE THERE IN THE BODY
    7 years ago by Mohseen Chawhan

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  141.  
  142. Sir frictional force have generally -ve work done and -ve work means gaining of energy how frictional force can gain energy
    8 years ago by Shivam pandey
    Ans 1 ->
    -ve work implies that the agent applying force must be gaining some energy. Not the force. In the case of friction. It is applied by the ground and ground gains energy in the form of dissipation energy. Hope it helped you. Thanks!
    7 years ago by akshat jain

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  143.  
  144. In this question as it is a work done in conservative field so it should be initialPE- finalPE NOT final-initial am i right?
    8 years ago by LAIBA NOOR
    Ans 1 ->
    No since here an external agent is doing the work thus {Work done=(Potential Energy)final-(Potential Energy)initial}
    7 years ago by Akshunn Trivedi
    Ans 2 ->
    7 years ago by Akshunn Trivedi

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  145.  
  146. as the body goes to some height then it will also gain some potential energy and thus i feel that the final mechanical energy should have k.f + final p.e .
    8 years ago by vivek
    Ans 1 ->
    Here used the basic work energy theorem which states that work one by allall the forces= change in kinetic energy So here work done by gravity is mg * length of the incline sin thita And work done by friction Add these two And equate it with change in kenergy U got ur answer As per ur opinion final mechanical energy is k.e plus p.e that's absolutely correct but it is consequence of the work energy theorem which states that Mechanical energy is constnt if there is no work by any nonconservative force Still u have any problem then don't hesitate to ask hope it will help u
    7 years ago by ansuman dixit

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  147.  
  148. Sir in above illustration work done.by tension must also be considered???
    8 years ago by Nitesh Guleria
    Ans 1 ->
    Considering both blocks as a system net work done by tension will be zero.
    8 years ago by Udit gupta

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  149.  
  150. Sir in this example . Why we have written force= - (potential gradient)
    8 years ago by Nitesh Guleria

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  151.  
  152. when a rigid body raise up its PE is also increase then why you said that rigid body contain only KE?
    8 years ago by rohit diwaker
    Ans 1 ->
    thats a case of conservative field
    8 years ago by Manav kapur

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  153.  
  154. sir in quset 1... there's a questn whose answer should be 5.76 but the option says 5.28...i'm pretty sure that the answer is 5.76 and i think there's a mistake in another questn..i got the answer as 3mv^2/4^x2....but the option says 3mv^2/4X..please rectify it or please let me know if i'm wrong..
    8 years ago by Aditya Prakash
    Ans 1 ->
    oh..there's a typing mistake...i got the answer as 3mv^2/4x^2
    8 years ago by Aditya Prakash
    Ans 2 ->
    Sir... Frictional forces have generally -ve work done and -ve work done means gaining of energy . how frictional force can gain energy.... I can't understand
    8 years ago by Shivam pandey
    Ans 3 ->
    Sir... Frictional forces have generally -ve work done and -ve work done means gaining of energy . how frictional force can gain energy.... I can't understand
    8 years ago by Shivam pandey
    Ans 4 ->
    You're right....the answer of that question is 5.76
    8 years ago by Abdullah Jafar

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  155.  
  156. first of all answer is wrong given M is greater than m sir took M is smaller than m i think there is small mistake sir
    8 years ago by akanksh

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  157.  
  158. How did you obtained the height of mass M ?
    8 years ago by aniket singh

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  159.  
  160. Sir if they are given us not to neglect the mass of the cord . Then what should be the approach ?
    8 years ago by Tejan Gupta
    Ans 1 ->
    Then you considered it and the weight of the cord also did a work i.e. its weight * extension of the cord
    7 years ago by ansuman dixit

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  161.  
  162. While using work energy theorem why the final kinetic energy is zero?Even though the force is minimum m2 must had gain some velocity.
    8 years ago by Sandip Kumar
    Ans 1 ->
    Friction opposed it.that's the reason
    7 years ago by ansuman dixit

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  163.  
  164. sir i want to ask a question. If disk is moving on a floor two types of kinetic energy should be there rolling and sliding we are solving this problem only with K.E. of centre of mass but there is no rolling kinetic energy is it right sir? please help me sir..??
    8 years ago by Amit Pardeshi

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  165.  
  166. Why didn't we find the area between 35 to 40?
    8 years ago by Divyansh Khurana
    Ans 1 ->
    since we have to take into consideration displacement from X=0 to X=35 m hope it helps!
    8 years ago by Abhijeet Kushwaha

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  167.  
  168. sir why we talk about potential energy in this example as potential is only been talk about in conservative field force ?
    8 years ago by Shubham Singh Kalyanwat
    Ans 1 ->
    spring force resulting from an ideal spring is a conservative force.
    8 years ago by vishwanath v pai
    Ans 2 ->
    in the final state the restoring force is perpendicular to motion of block so why isnt the work done by the spring in the final state o
    7 years ago by charan
    Ans 3 ->
    in the final state the restoring force is perpendicular to motion of block so why isnt the work done by the spring in the final state o
    7 years ago by charan
    Ans 4 ->
    in the final state the restoring force is perpendicular to motion of block so why isnt the work done by the spring in the final state o
    7 years ago by charan
    Ans 5 ->
    in the final state the restoring force is perpendicular to motion of block so why isnt the work done by the spring in the final state o
    7 years ago by charan
    Ans 6 ->
    in the final state the restoring force is perpendicular to motion of block so why isnt the work done by the spring in the final state o
    7 years ago by charan
    Ans 7 ->
    in the final state the restoring force is perpendicular to motion of block so why isnt the work done by the spring in the final state o
    7 years ago by charan
    Ans 8 ->
    7 years ago by charan
    Ans 9 ->
    7 years ago by charan
    Ans 10 ->
    7 years ago by charan

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  169.  
  170. A block of mass M is connected rigidly with a smooth wedge (plank) by a light spring of stiffness K. If the wedge is moved with constant velocity V, find the work done by the external agent till the maximum compression of the spring. ImageUrl :- https://embibe-cdn.s3.amazonaws.com/resources/images/EM0014759_Question_1.jpg
    9 years ago by Kshitij Kumar Singh

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  171.  
  172. A block of mass M is connected rigidly with a smooth wedge (plank) by a light spring of stiffness K. If the wedge is moved with constant velocity V, find the work done by the external agent till the maximum compression of the spring.
    9 years ago by Kshitij Kumar Singh

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  173.  
  174. Sir please explain ..why don't the work energy theorem incorporates the complete dynamical information of Newton's second law .....
    9 years ago by Kamal

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  175.  
  176. a single conservative force F(x) acts on a 1.0 kg particle that moves along the x-axis. The potential energy U(x)is given by U(x)= 20+(x-2)^2 where x is in metres. At x=5.0m the particle has kinetic energy of 20 J. The greatest value of x between which the prticle can move is:
    9 years ago by taniiiroxx

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  177.  
  178. Sir in the final answer in denominator it should be m1+m2
    9 years ago by Mohak Sharma
    Ans 1 ->
    if any one did not understand solution please go to https://www.youtube.com/watch?v=_lpSFr1cPks&list=PL3Wi397dlS-Eb8RuIc3-i3iZYRjw910Tk&index=10
    8 years ago by akanksh
    Ans 2 ->
    Yes @Mohak Sharma is right :)
    8 years ago by vishwanath v pai

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  179.  
  180. Sir why this was not done Body will be lifted till a height till which mg= F . This gives us the height till which body will be lifted =1/2b. But according to your solution it is 1/b. Please tell me where am i wrong .
    9 years ago by Mohak Sharma
    Ans 1 ->
    When body reaches to the position where mg=F it will gain some kinetic energy and will further go up thats why height will be more....
    9 years ago by Physics Galaxy
    Ans 2 ->
    see mahak sharma when mg=F accn = 0 please note a very imp point that when accn = 0 that does not mean velocity = 0 even at y=1/2b there velocity is not zero check if u want put in the expression
    8 years ago by akanksh

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  181.  
  182. Sir if i displace a block by applying a constant force on it * on a surface where there is friction * on a frictionless surface will the work done by me will the same in both cases= F d cos theta
    9 years ago by Mohak Sharma
    Ans 1 ->
    Yes. Work done by the external force is always force x displacement of point of application of force...BUT in case of rough surface some -ve work will be done by friction which is dissipated so gain in kinetic energy of block will be less compared to first case.
    9 years ago by Physics Galaxy

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  183.  
  184. Sir is there something like work done by an impulse? If yes then how is it calculated?
    9 years ago by Mohak Sharma
    Ans 1 ->
    It is the energy imparted by the impulse to the body on which impulse is applied...
    9 years ago by Physics Galaxy

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  185.  
  186. Sir why isnt the work done in moving the block added to the answer that is force × disp. of block= F L tan theta?
    9 years ago by Mohak Sharma
    Ans 1 ->
    As the block is displaced slowly, it will not gain any kinetic energy so total work done by force will be stored as potential energy of spring so it will give the same result... we cannot include same energy twice...
    9 years ago by Physics Galaxy

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  187.  
  188. Sir i am unable to understand how you calculated the work done by friction(you said that according to concept video work done by friction only depends on the horizontal distance) .Also, i am unable to find the video related to this concept. Please help.
    9 years ago by Mohak Sharma
    Ans 1 ->
    Work is the force multiplied by the displacement of point of application of force in the direction of force... Here same calculation is done for elemental displacements and then total work can be calculated...
    9 years ago by Physics Galaxy
    Ans 2 ->
    Sir but friction is a non-conservative force.So work done by friction should be force multiplied by pi*r/4
    8 years ago by Karan Singh
    Ans 3 ->
    Yes, sir, I agree. If frictional force is nonconservative and as written in your book path dependent then why have we taken simply R? Not pi*R
    6 years ago by Ayushi Jain
    Ans 4 ->
    The catch here is that the magnitude and direction of frictional force is changing with motion of the block. You consider the block at an angle theta with horizontal. Hence the normal reaction will be mgcos(theta). At this instant the corresponding frictional force will be the above times 'mu'.Now in further motion if block is displaced by an angular position d(theta) then the elemental work done by friction will be mu*mg*Costheta*R d(theta). Now integrate this from 0 to pi/2. You will get the answer.
    6 years ago by Mohak Sharma

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  189.  
  190. A rifle bullet loses (1/20)th of its velocity in passing through a plank. Assuming that the plank exerts constant retarding force, the least number of such planks just required to stop the bullet is ?
    9 years ago by SAKSHI AGARWAL
    Ans 1 ->
    Here you can calculate the width of plank by using speed equations in terms of constant retardation and then to reduce the velocity to zero you can find out the total distance to be traveled by the bullet at that retardation and divide this distance with the width of plank. This will give you the no of planks...
    9 years ago by Physics Galaxy

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  191.  
  192. Q-Two blocks of masses m1 and m2 are connected by a spring of stiffness k.The coefficient of friction between the blocks and the surface is n.find the minimum constant horizontal force F to be applied to m1 in order to slide the mass m2.(initially spring is in its natural length).
    9 years ago by shubham singh
    Ans 1 ->
    You can use W-E theorem for this Que. When F is applied on m1 it compresses the spring to the value x=n(m2g)/k in order to slide m2. Now for this you can use the equation - Fx - n(m1g)-(0.5)kx^2=0, you will get it by solving this eqn...
    9 years ago by Physics Galaxy

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  193.  
  194. why when conservative forces do work that energy changes to potential energy only why not kinetic energy
    9 years ago by hemanth goud
    Ans 1 ->
    When work is done by conservative forces the potential energy of the force field increases or decreases depending if work is negative or positive respectively... If this work is done by conservative forces on a rigid body same amount of energy changes the kinetic energy of that body... you are getting confused between work of force field or that of an external body... pl watch again and try to understand carefully...
    9 years ago by Physics Galaxy

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  195.  
  196. in ucm if force is perpendicular to velocity then why the work done by force is zero?
    9 years ago by mahesh
    Ans 1 ->
    Work is calculated as the product of force and displacement of point of application of force in the direction of force, if force is acting normal to velocity, displacement in the direction of force will be zero so work will be zero by this force... To understand in detail, you can watch videos of 'Work-Energy-power' topic under 'Mechanics' section thoroughly...
    9 years ago by Physics Galaxy

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  197.  
  198. sir, shouldn't we consider mgh at the top of wedge (at B)
    9 years ago by sai krishna
    Ans 1 ->
    the force acting downward is mgsin60 which is already taken care of . The force acting downward will not be mgh but mgsin60. because it is an inclined plane.
    9 years ago by amit kawad

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  199.  
  200. we consider that spring is massles .what if the spring has mass.how do you do it
    9 years ago by ramesh nagda
    Ans 1 ->
    during problems that regard vertical springs take weight of spring mg in consideration
    9 years ago by Ch Vishal

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