New to the forums, and I have no experience with LaTex, so if I've done something wrong, I'll try to edit it in a bit.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A 100 g puck attached to a string is revolving in a 20-cm-radius circle on a frictionless table. The string passes through a hole in the center of the table and is tied to two 200 g weights.

a) What speed does the puck need to support the two weights?

b) One of the two 200 g weights is cut free. What will be the puck's speed and the new radius of its trajectory after this weight is gone?

2. Relevant equations

[tex]T = m_2g[/tex] (Equating tension force with gravitational force of the two weights)

[tex]v^2 = \frac{m_2gr}{m_1}[/tex] (Rearranging for the speed of the puck)

Not sure which others I need...

3. The attempt at a solution

So, I managed to solve for the first part of the problem (this question has answers in the textbook, so I use them to verify my results).

However, I'm not sure how I'm supposed to approach the second part of this question. I know that the forces are no longer in balance, but I'm not sure how I use conservation of momentum in this system.

I tried using [tex]I_iw_i = I_fw_f[/tex], but that gave me the wrong answer.

I do know that because of the momentum it already has, the radius will increase and the speed will drop, but I really don't know how to approach this, and my TA is pretty anti-social and hard to track down.

Any help on the right approach or formula would be greatly appreciated. Thank you for your time. :D

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# Homework Help: Conservation of Angular Momentum of Puck Problem

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