Question

give reason of the following a load on thief back does not apply any force on him when he jumped from upper story of house

Answer 1

This is due to the effect of free-fall.

When the thief and the load on his back are in free-fall, gravity attracts them with the same rate. Moreover, according to Einstein's Theory Of Relativity, gravity is not a force but acceleration itself. So, the thief doesn't feel the weight of the load on his back, and he also doesn't feel his own weight either.