Hello, I'm having trouble with solving for the centripetal force. Some questions in my textbook don't give the velocity and radius, so the centripetal force is a bit harder to calculate. There are three main scenarios which I am having trouble with:  A girl has a ball in her hand connected to a string. The ball travels in a circular path, such that the plane of the circle lies perpendicular to the plane of the earth.  A girl now swings the ball in a circular path, so the plane is parallel to the earth.  A car drives a long a raceway in a circular loop. For each of these scenarios, what would be the centripetal force and how would you solve for it, generally? I'm having trouble solving for this, especially when trig functions are used. Thanks, and any help would be great!