The screen with the force vs. time graph is a little hard to see in the video, so the graph is reproduced below.

Q1. Describe the motion of each cart before and after the collision.

Q2. What observations do you make about the force that each cart exerts on the other cart? 

Q3. You should have found that the force graphs look like mirror images of each other. At each instant during the collision, the force exerted on the second cart by the first cart was equal in magnitude but opposite in direction to the force exerted on the first cart by the second. The two forces you have measured are referred to as interaction forces. Predict: What do you think the graphs will look like if one cart is at rest before the collision? Sketch your predicted force vs. time graphs and explain

Help answer Q1 ,Q2, and Q3. Thanks