# Work Energy Theorem in Spring Block System

1. Feb 2, 2016

### SDewan

Just got confused that while applying the Work - Energy Theorem in a vertical Spring-Block system performing SHM (considering no other external forces other than gravity), when I apply the theorem from equilibrium position, do I consider the work done by gravity?

2. Feb 2, 2016

### BvU

Hello SD,

In principle: yes.
In exercises it's often easier to work with the net force (i.e. the vector sum of the spring force and the gravitational force) and the associated net potential energy ${1\over 2} kx^2$ where $x$ is the extension minus the equilibrium extension.

If you want this clearer, you may want to provide a complete problem statement for the exercise that confused you.

3. Feb 2, 2016

### SDewan

Yea I understood that it will be better to apply the W-E Principle from the relaxed length of the spring, rather than the equilibrium position.
I feel that it is simpler to take all forces into consideration. i.e. gravity, spring force and the kinetic energy.
I have got the clarity, thanks a ton!