If a man of mass M jumps to the ground from a height h and his centre of mass moves a distance of x during the impact, the average force acting on him (assuming his retardation to be constant during his impact with the ground) is
Mghx
Since the centre of mass moves through a distance x, the average force F is given by Fx=Mgh
⇒F=Mghx
Hence, the correct choice is (a).