A train is rounding a curve, that is part of a circle with a radius R. A pendulum on the train swings out to an angle θ throughout the turn. What is the speed of the train?
I'm not sure what the centripetal force on the pendulum is here. There is a tension force pulling it up and a gravitational force pulling it down. What other forces are there? It's not touching anything so it can't be a normal force or a static friction force. Once I know what this force is, I can easily do the rest of the problem, but I have no clue what it is.