Energy and its Relation with Work

When you do work, you spend energy and more energy is required to do more work. The capacity of a body to do work is determined by the energy possessed by it.

Energy possessed by a body = Total work that the body can do

Energy has the same unit as work, i.e., joule denoted by J.

However, conversion of 100% of energy may not always be practicable, because, in the process of conversion of energy into work some energy may remain unused or may be wasted.