An object of mass 4 kg is raised to height of 5 m above the ground. What is its potential energy ? If the object is allowed to fall, find its kinetic energy when it is half way down.

Explanation

m = 4 kg, h = 5 m, g = 10 `m//s^(2)`
Potential energy = mgh `=4 times 10 times 5=200J`
If object is allowed to fall, then we have to take half of distance.
u = 0, h = 2.5 m, a = + g = 10 `m//s^(2)`
`v^(2)-u^(2)=2gh rArr v^(2)=2 times 10 times 2.5 rArr v^(2)=50`
Kinetic energy `=1/2mv^(2)=1/cancel(2) times cancel(4)^(2) times 50=100J`.
`therefore` At half of distance the kinetic energy = 100 J.