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2004 Question 2c

Jonny-Sensei

Posted 16 May 2006 - 06:35 PM

QUOTE
A yo-yo consists of two discs mounted on an axle. A length of string is attached to the axle and wound round the axle.

With the string fully wound, the yo-yo is suspended from a horizontal support.

The yo-yo is released from rest and rotates as it falls.

The string is funny unwound at the yo-yo's lowest point.

The yo-yo then rises, rewinding the string.

© When the yo-yo is at its lowest point, it has an angular velocity of 120 rad/s.
Calculate the maximum height to which the yo-yo could rise as it rewinds the string.

(Data from other questions: mass=0.1kg, radius=0.05m, moment of inertia=2.5x10^-4)


I've tried two methods so far:

(1) Changing angular velocity to linear velocity, then using  v^2 = u^2 + 2aS

(2) Ep = Rotational Ek  mgh = 1/2Iw^2

but both result in 1.84m, which is twice the value given in the answer booklet (0.92m. in case you can't divide by two smile.gif) If anyone can help, I will love you forever wink.gif

colinH

Posted 16 May 2006 - 07:42 PM

click this link for the sqa marking instructions and you will find the answer! biggrin.gif

Good luck tomorrow!!!

http://www.sqa.org.uk/files_ccc/04mi_Physics_AH.pdf

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