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mikefitz

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**A pendulum of length 130 cm swings with an amplitude of 2.1 cm. Its mechanical energy is 7 mJ. What is the mechanical energy of the same pendulum when it swings with an amplitude of 3.9 cm?**

Well I know that energy is conserved in such a system; what I don't know is how to calculate KE and PE of this pendulum (also, I know that mass is independent of frequency). I've read that total ME is proportional to the square of the amplitude, though I'm not sure how to work that into my solution.

My book does have a chapter on simple pendulums, with equations for calculating the period, frequency, and angular frequency - what it does not have are equations for calculating a pendulums energy. Any help? thanks