A pendulum consists of a 3.1 kg stone swinging on a 4.2 m string of negligible mass. The stone has a speed of 7.9 m/s when it passes its lowest point.
(a) What is the speed when the string is at 50 ? to the vertical?
(b) What is the greatest angle with the vertical that the string will reach during the stone's motion?
(c) If the potential energy of the pendulum-Earth system is taken to be zero at the stone's lowest point, what is the total mechanical energy of the system?