Solved example 6: I found this example to be very useful. I am confused as to why the required force on the large block is F = a(7m).= a(4m + 2m + m). The fbd for the large block does not have any interaction with block A (mass m) in the horizontal direction. I found that the force on the large block should be F = a (4m + 2m). Is this correct? I looked up this example when trying to solve the situation when the two smaller blocks are accelerating relative to the large block, and I do not see how the three blocks can be considered together even when the relative acceleration is zero. The interpretation that the system can be taken as a whole seems to ignore the fact that the force of gravity is also acting on block B and, importantly, via tension on block A. Please let me know where I am going wrong here. Thanks, for your really useful website.
9 years ago
by
Paul Moore