A block (A) collides with block (B). The blocks were in contact for 0.25 seconds. So what is the force exerted on block (A) by block (B)? I used the formula for impulse and set it equal to the momentum. But it requires a change in velocity for it to work. I already know the velocity of each block before and after the collision, so since its the force on (A) by (B), the change in velocity in the formula is the velocity of (B) before and after the collision, right?