(adsbygoogle = window.adsbygoogle || []).push({}); 1. We have a cylinder of Mass M rotating about its axis. String is wound around it. Other end is connected to a spring. A mass m is attached to the spring.

The problem is to find the Lagrangian. My only issue is with finding the potential energy. The problem asks to use the distance of the mass m from center of axis of cylinder to be 'y' and length of spring to be 's'.

If I take downward positive, I can write,( with U=0 at axis of cylinder) I can write,

U=mgy + 1/2ks^2

But if I take downward negative, U= -mgy+1/2 k s^2

So using two coordinate systems will result in two different end answers for equations of motion.

Any thing wrong in what I am doing

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# Homework Help: Finding the potential energy

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