5. a. A 3600 kg boat is moving with a speed of2.8nLr"'s. A much smaller 100 kg jet ski has half the amount of kinetic energy of the boat. What is the speed of th=e jet ski? a. How much work is done by gravity when a ?.64 kg boulder falls to the ground from the top of a 33.4 n1 tall cliff? a. A 0.2kg apple on an apple tree has a potential energy of 10.1. It falls to the ground, converting all of its PE to kinetic energy. What is the velocity of the apple just before it hits the ground? b. How long will it take an 850-kg car with a useful power output of 40.0 hp (1 hp = 7'46 W) to reach a speed of 15.0 nus, neglecting friction