A 80 kg student consumes 2500 cal each day and stays the same weight. One day, he eats 3500 cal and, wanting to keep from gaining weight, decides to "work off" the excess by jumping up and down. With each jump, he accelerates to a speed of 2.8m/s before leaving the ground.
How many jumps must he make? Assume that the efficiency of the body in using energy is 25%?