The unstretched length of a spring is 5 inch. The spring expands from a length of 2 inch to a length of 4 inch. The spring constant is 100 lb. in. The work done (by the spring force) on a particle...

The unstretched length of a spring is 5 inch. The spring expands from a length of 2 inch to a length of 4 inch. The spring constant is 100 lb. in. The work done (by the spring force) on a particle attached to the spring is inch middot lb. a.200 b.400 c.-400 d. -600