An object of mass 40kg is raised to a 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 halfway down. (Take `g=10ms^(-2)`.)

Answer

The potential energy is 2000 J. The kinetic energy is 1000 J.

Explanation

Here, `m=40kg,h=5m,g=10ms^(-2),u=0,E_(p)=?`
Potential energy `E_(p)=mgh`
`=40kgxx10ms^(-2)xx5m`
`=2000J`
When it is allowed to fall, its potential energy gets converted into kinetic energy.
When the object is halfwary down `s=h=2.5m`
Let its velocity be `vms^(-1)`.
`v^(2)-u^(2)=2gh`
`therefore v^(2)-(0)^(2)=2xx10xx2.5`
`therefore v^(2)=50`
Kinetic energy `E_(k)=(1)/(2)mv^(2)`
`=(1)/(2)xx40xx50=1000J`