John (m=85 kg) performs a vertical jump. He starts from standing still and then bends his knees and

pushes against the floor before takeoff. The duration of push off before takeoff is 0.25 sec. His takeoff

velocity is 1.8 m/s. Calculate (1) the average ground reaction force Fg,y during the push off, (2) is his

jumping height greater than 0.4 m?