Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

A ball of mass M is attached to the end of a string...
My attempt (if it matters):
The initial period is given by $T_X = \frac{2\pi X}{v}$ for some $v$.
The new period is given by $T_Y = \frac{2\pi Y}{v}$ for the same $v$.
$Y = \frac{X}{2}$, so $T_Y=\frac{\pi X}{v} = \frac{T_X}{2}$

However, the correct answer is $\frac{1}{4}T$. Can somebody explain this to me?

share|improve this question

1 Answer 1

up vote 2 down vote accepted

OP writes in the question formulation(v2):

[...] for the same $v$.

Hint: The speed of the ball is not conserved. Think instead about

  1. why the angular momentum of the ball is conserved, and

  2. what angular momentum conservation implies.

share|improve this answer
1  
$\omega$ is not angular momentum –  Bernhard May 1 '12 at 14:57
    
Many thanks; I got it now. –  highphi May 1 '12 at 15:03

Your Answer

 
discard

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.