The boy cannot lift this box.

An open lift is coming down from the top of building at a constant speed v=10m//s . A boy standing on the lift throws a stone vertically upwards at a speed of 30 m/s w.r.t. himself. The time after which he will catch the stone is:

Consider the situation as shown in the figure. The boy of mass M holds the light rope and the system is at rest. If m is mass of the box, find the force exerted by the boy on the rope and contact force beteween the boy and the box.

A box of mass M is at rest on a horizontal surface. A boy of mass m (lt M) wants to push the box by applying a horizontal force on it. The boy knows that he will not be able to push the box as the coefficient of friction mu between his shoes and ground is almost equal to that between the box and the ground. He decides to run, acquire a speed u and then bang into the box. After hitting the box, the boy keeps pushing as hard as possible. What is the maximum distance through which the box can be displaced this way ?

In the previous problem if M=80kg and m=410kg and the boy pulls the rope such that the system (boy+box) moves upward with acceleration 5m//s^(2) ,find the force exerted by the boy and contact force between the boy and the box.