Question

Calculate the potential energy of an object of mass 50 kg resied to a height of 4m above the ground. If the object falls down, what is its kinetic energy when it has fallen through 2m? (take g-10m/s2)

Answer 1

A body has potential energy (mgh) due to its height above the ground and kinetic energy (1/2(mv²)) because of its motion.

At a height of 4m,potential energy =mgh=50 x 10 x 4=2000J

When a body falls down from a height, its 'stored' potential energy starts decreasing (as h decreases) and kinetic energy starts increasing (as v increases). At half the height (here h = 2m), the potential and kinetic energies are equal.

So kinetic energy=potential energy=mgh=50 x 10 x 2=1000J