Figure 1) shows a 100 g puck revolving at 200 rpm on a 20-cm-radius circle on a

Question

Figure 1) shows a 100 g puck revolving at 200 rpm on a 20-cm-radius circle on a frictionless table. A string attached to the puck passes through a hole in the middle of the table. The end of the string below the table is then slowly pulled down until the puck is revolving in How many revolutions per minute does the puck make at this new radius? Express your answer using two significant figures Figure ?1of1 ? u270 rpm 100 g SubmitPrev Previous Answers Request Answer 20 cm X Incorrect; One attempt remaining: Try Again Provide Feedback

Explanation / Answer

It's a conservation of momentum problem

So you're going to fine the momentum at the radius of 20 cm, and use that to find w at the radius of 15 cm (if it is the final radius, as you have not mentioned it).

I= mr^2

L(momentum) = Iw

So,

m*r1^2 * w1 = m * r2^2 * w2

(20)^2 * 200 = 15^2 * w2

=> w2 = 360 rpm

[If final radius is something other than 15cm, then use that value]

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