Question

http://imgur.com/Fv4kHq2 physics question?

Answer 1

Well, first we see that the two blocks are not moving with respect to one another (they aren't getting closer together, nor further apart), correct?

Answer 2

Accepting that, we can just look at the forces in the system. A force F is pushing on the large block. The large block is pushing on the small block. Both blocks are accelerating by 2m/s^2.

Since the two blocks are not separating, there's no outside force pushing them apart, and we can just use Newton's laws to find the answer. First, we use "For every action there is an equal, but opposite, reaction." This means that when the big block pushes the little block by some force, the little block pushes back by the same amount.

All of this is rather long winded, but it gets us to where we can finally calculate the answer. Do you see how to do it?

Answer 3

f=ma = 5*2 = 10 N?

Answer 4

Close. We need to find the force that is accelerating the small block. This will be the same magnitude as the force of the small block pushing on the large.