A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is.

Options

A. constant and equal to mg in magnitude
B. constant and greater than mg in magnitude
C. variable but always greater than mg
D. at first greater than mg , and later becomes equal to mg .

Answer

D

Explanation

When man is squatting on the ground , then in order to get straight up and stand , the man exerts a variable force ( say F ) on the ground to set his body in motion . This force is in addition to thef orce due to its weght on the ground , i.e mg . Therefore , force of reaction of ground man is more . When he stands up straight , reaction on the ground becomes mg and the additional force (F) becomes zero .