Question

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.

Answer 1

a = F/m [Here F is force applied by ground on man]

Here F is impulsive for a so mg may be neglected.

(b) Since, contact point does not move. Hence, work done by normal reaction is zero.