A man whose mass is m kg jumps vertically into air from a sitting position in which his centre of mass is at a height h1 from the ground. When his feet are just about to leave the ground his centre of mass is h2 from the ground and finally rises to h3 when he is at the top of the jump.
(a) What is the upward force exerted by the ground on him treating it as a constant?
(b) Find work done by normal reaction from ground.