A cart with a spring on the end of it is moving right (in the positive x direction) on a frictionless air track as shown in the figure at the right. The initial position of the cart is arbitrary. It keeps going until it hits a wall, the spring compresses, and the cart bounces off the wall and moves in the opposite direction. Select all the graphs that could represent each of the following quantities as a function of time. (In each graph, the axes cross at the origin of the two coordinates.) Put N if none of the answers work.