- #1
clementc
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Homework Statement
Hey guys,
I just read Physics, by Halliday, Resnick and Krane. There's a chapter on rotational dynamics, and the example goes like this:
A yo-yo of total mass M = 0.24kg consists of two disks of radius R = 2.8cm connected by a thin shaft of radius R0 = 0.25cm. A string of length L = 1.2m is wrapped around the shaft. If the yo-yo is thrown downward with an initial velocity of v0 = 1.4m/s, what is its rotational velocity when it reaches the end of the string?
Homework Equations
[tex]KE = \frac{1}{2} mv^2[/tex]
[tex]Rotational KE = \frac{1}{2} I{\omega}^2[/tex]
[tex]I of a cylinder = \frac{1}{2} mr^2[/tex]
Conservation of energy
The Attempt at a Solution
The way the book did it was really strange and long, so I tried doing it using conservation of energy, but got the wrong answer. Can anyone see what's wrong here?
[PLAIN]http://img151.imageshack.us/img151/6251/rotational.png
Their answer was 610 rad/s, but I really don't know where I went wrong here. Any help would be very greatly appreciated. Thanks!
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