7. A string pulls horizontally on a cart so that it moves at increasing speed along a smooth horizontal surface. When the cart is inoving medium-fast, the pulling is stopped abruptly. (a) Describe in words what happens to the cart's motion when the pulling stops. (b) Illustrate your description with motion diagrams, force diagrams, and position-versus-time and velocity versus-time graphs. Indicate on the graphs when the pulling stopped. What assumptions did you make? Solving the previous problem, your friend says that after the string stops pulling. the cart starts slowing down. (a) Explain why your friend would think this way. (b) Do you agree with him? Explain your opinion. (c) Ex- plain how you can design an experiment to test his idea