question_answer 33)

                  A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is                 (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) In the process of getting straight up and stand from squatting potion, the man exert a variable force (F) on the ground to set his body in motion. This force is in addition to the force required to support his weight (mg). Once the man is in standing position, F becomes zero.