Please help; I think my professor might be wrong, A cart travels toward an inelastic barrier at a constant speed v. On the cart is a pendulum that is not oscillating before the collision. (It is hanging straight down and traveling at the same speed as the cart.) The cart then collides (perfectly inelastically) with the barrier and comes to a complete stop instantaneously. The pendulum support is fixed to the cart and comes to a complete stop, but the pendulum is free to swing. Question: What is the maximum angle through which the pendulum can swing for an arbitrary v? The puzzle: My professor contends that there is a maximum angle, and I contend that there is not (the pendulum will swing in circles for a high enough v.) If you think my professor is wrong, I agree, but that's not the question. If you think I am wrong, please be specific about the physics. The question is what train of thought (or physical approximation) would lead to his conclusion that there is a maximum angle to which the pendulum can swing? I cannot ask the professor, as he is trying so hard to be coy. Thanks.