According to Newton's Second Law of Motion, the net force is equal to the product of the system's mass and acceleration. There are two forces acting on a jumper once he jumps: gravitational force and upward force. The solution is as follows:
Net Force = mass * acceleration Upward Force - Gravitational Force = mass*4*gravity F - mg = 4mg F = 4mg + mg F = 5mg
Thus, the force must be five times greater than the gravitational force.
