Numerical on gravitation
Here is a solved numerical example on Gravitation:
Question:
An object of mass 50kg is raised to a hight of 10m above the ground. Find the potential energy of the object at the higest point. If the object is allowed to fall freely, what is its kinetic energy when it is half way down? give reason to justify your answer.(g=10m/s)
Answer:
Gravitational potential energy is given by the expression,
W = mgh
where,
h = Height above the ground = 10 m
m = Mass of the object = 50 kg
g = Acceleration due to gravity = 10 ms-2
W = 50 × 10 × 10 = 5000 J.
At half-way down, the potential energy of the object will be, 
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 also be 2500 J.