A pendulum consists of a 3.1 kg stone swinging on a 3.8 m string of negligible mass. The stone has a speed of 7.9 m/s when it passesits lowest point. (a) What is the speed when the string is at 57° to the vertical? (b) What is the greatest angle with the vertical that the string will reachduring the stone's motion? (c) If the potentialenergy 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?