A body of mass m is moved from ground to a height h. If force of gravity on mass of 1 kg is g newton, find:

(a) the force needed to lift the body,

(b) the work done in lifting the body and

(c) the potential energy stored in the body.

(a) When a body of mass m is raised to height h above ground, a force is applied.

Force needed to lift the body (F) = weight of the body

If g is the force of gravity on mass of 1 kg, then the force of gravity on mass m kg will be mg N.

F = mg N

(b) Force = mg N; distance moved = h
Work done = force x distance moved = mg x h = mgh joule

(c) The work done against the force of gravity in lifting the body to a height h is stored in the body in form of its gravitational potential energy.

Potential energy (U) = mgh joule