Question

Define potential energy.Write an expression for potentialenergy.Write the si unit of potential eneryg

Answer 1

Thank you for asking this question, I'll try and answer in the simplest way possible. 
Potential energy is basically the energy of the body due to its position or its compressed state, the expression for potential energy is PE=MGH where M is mass, G is the force of gravity and H is the height at which the object is placed. The si unit for potential energy is joule. For example and object placed at one meter above the ground weighing 1 kg on the surface of earth with have the potential energy of 9.8 joules.
There is another kind of potential energy which is their due to the compression in an object for example like that of in springs. This is called the elastic potential energy. 
Hope this answers your question well.

Answer 2

The energy possessed by a body due to its shape or position or configuration is called the potential energy.
p.e.=mgh
The SI unit for p.e. is Joule.