Under which force energy is not conserved?

A 2 kg body falls from infinity to the surface of earth. What will be the kinetic energy of the body on reaching the surface of Earth (Assume escape velocity to be 104 ms-1)?

A bird resting on the floor of an air-tight box which is being carried by a boy, starts flying. The boy will feel that the box is now:

A body in satellite orbiting round the earth is weightless because:

A body is taken from the earth's surface to the moon, the weight of the body will be zero at a point where force of attraction due to:

A body of 2kg is suspended from the ceiling of an elevator moving up with an acceleration 'g' its apparent weight in the elevator will be: