Gravitational potential energy is given by the expression, P.E= mgh
where, h is the vertical displacement = 5 m
m is the mass of the object = 40 kg
g is the Acceleration due to gravity = 9.8 ms−2
∴P.E=40×5×9.8=1960 J.
At half-way down, the potential energy of the object will be 19602=980 J.
At this point, the object has an equal amount of potential and kinetic energy.
This is due to the law of conservation of energy.
Hence, half-way down, the kinetic energy of the object will be980 J.