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ronynelson28@yahoo.com
Joined: 13 Mar 2012 Posts: 1 Location: woobridge

Posted: Tue Mar 13, 2012 8:34 pm Post subject: CIRCULAR MOTION 


I'M HAVING trouble finding the radius for my question
A rock on a string is swung in a circle. The centripetal acceleration of the rock is 5.21 meters per second square. The time period for one rotation is 5.5 seconds.
What is the length (radius) of the string? 

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hepcj Site Admin
Joined: 23 Jun 2007 Posts: 125

Posted: Thu Mar 15, 2012 8:04 pm Post subject: 


With this question you need to consider the centripetal force
F = m*r *omega^2
and this force is equal to = m a
equating
m a = m r omega^2
the mass cancels to give,
a = r omega^2 (1)
The period in terms of omega is T = 2 pi omega
which means omega = T/(2 pi)
then substitute into (1)
This gives a = r (T/(2 pi))^2 = r T^2/(4*(pi^2))
now you have everything you need to calculate the radius r if you rearrange to make r the subject in terms of a and T. 

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