2) On a tabletop rests a heavy block (A), with a lighter block (B) on top
of it (see figure at right). We will use T to represent the tabletop, and F to
represent the finger pushing on the stack of blocks. Consider the forces
B
NAB
fTA
FAB
NEA
fBA
NBA
A
In each of the three scenarios below, specify the directions (left,
right, up, down) of the above forces. If any of the forces are zero in a
given scenario, state so directly. Always ignore air resistance.
a) You start pushing on block A, but the block is too heavy and doesn't move. In this instant,
where you're pushing but block A isn't moving what are the directions of each of the forces
above? Support your argument with free body diagrams.
b) Now you add some oomph to your push and block A starts moving. Block B moves with it
and doesn't slip. Both blocks are now speeding up in tandem. What are the directions of each
of the forces above? Support your argument with free body diagrams.
c) Now you ease up a little so the blocks move at a constant velocity. As before, the blocks
move together - block B isn't slipping. While the blocks are moving with constant speed,
what are the directions of each of the forces above? Support your argument with free body
diagrams.
