1. The Question Unable to find the work done by spring on the object sliding down the rod as shown below: 2. Relevant equations Work Done by Spring Force : -1/2 * KΔx2 --(1) where k = Spring Constant Δx = Change in Spring Length 3. Where the problem occurred While seeing the solution of the problem, it was mentioned that we can simply take WSpring = -1/2 * K(X22-X12) --(2) But my problem is that if the position of ring on rod is changing, the angle of spring with the rod is changing and thus the force components on rod is changing, then how the usual formula Work Done by Spring Force : -1/2 * KΔx2 is also valid for the given condition. PS: I also tried to understand this using concept of conservative force, but couldn't get it. Thanks!