Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

A solid disk and a solid sphere each of them has the same mass and same kinetic energies, which one is faster?

share|cite|improve this question
I wish to emphasize what John said below: we don't do homework here. Please ask about concepts. – dmckee Jul 13 '12 at 18:00

As with your previous question, How we can find the kinetic energy?, we can't just answer homework questions but we can discuss how to go about solving them.

The disk and sphere have the same kinetic energy due to translation (bulk motion in space), so it's just the energy of rotation that's different. The disk and sphere will have different angular velocities because for the same mass they have different radii. Also the expressions for the angular kinetic energy are different. As before, a quick Google will find the you relevant equations. Ask here if you still run into difficulties.

share|cite|improve this answer
Good answer, and good job addressing the question at the conceptual level. I hope you don't mind my tweaking the language a bit. – dmckee Jul 13 '12 at 17:58

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.