Question

Why work done by external force is not always equal to potential energy?

Answer 1

Answer:

Yes

Explanation:

This statement is absolutely true.

• Usually we say that work done by a force is equal to the change in Kinetic energy not potential energy (from Work Energy theorem) cause a body can do work if it remains on the same potential.

• For example:  If a body moves from a horizontal position A to B by the application of force F then potential of the body remains same as its on the same level but kinetic energy changes.
• By same level we mean that the potential isn't changing as potential depends on the level or surface chosen as zero potential

• Work done by all forces=change in kinetic energy

       W=ΔKE

• Another point here is that we can equate the work done by the force with potential energy if and only if no energy is lost during the process in the form of heat,light,sound,friction etc

• For example : If a body is thrown upwards then the gain in potential energy is only conserved when there is no air drag.

Hope this helps.