# Energy conservation in simple pendulum

1. Jul 5, 2011

### imjudit

Hello everyone! I've found this problem in my exercises book, and I'm having slight troubles solving it.
"Consider a simple pendulum with mass m, on a string with l length. Considering that the position of pendulum is determined with the angle $\theta$ and noting that the string DOES NOT do any work, considering all the forces acting on the pendulum show that the energy conservation law is applied"

Well, I know how to prove that the ECL is applied without using the forces (considering that the Ep is 0 at the lowest point, and that the Ek is 0 at the highest).
Any ideas?