A boy puts a heavy box of mass M on his head and jumps down from the top of a multistoried building to the ground. How much is the force exerted by the box on
his head during his free fall? Does the force greatly increase during the period he balances himself after striking the ground?
When the boy jumps from the building, the acceleration of boy as well as the box become g (acceleration due to gravity). Hence the net force is exerted by the earth and none of them exert any contact force.
Yes, the force greatly increases when he strikes on the ground because it becomes impulsive force and the boys head exerts a huge force which reduces the momentum of the box to zero in a very short period of time.