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Please Help - A circus Trapeze...

by mirandasatterley
Tags: circus, trapeze
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mirandasatterley
#1
Nov6-06, 06:08 PM
P: 62
Any help with the following question would be appreciated. Please keep in mind that i'm not very good with physics.

"A circus trapeze consists of a bar suspended by two parallel ropes, each of length l, allowing performers to swing in a vertical circular arc. Suppose a performer with a mass m holds the bar and steps off an elevated platform, starting from rest with the ropes at an angle theta_i with respect to the vertical. Suppose the size of the performer's body is small compared to the length l, she does not pump the trapeze to swing higher, and air resistance is negigable.
A) Show that when the ropes make an angle theta with the vertical, the preformer must exert a force: mg(3 cos theta - 2 cos theta_1), so as to hang on.
B) Determine the angle theta_i for which the force needed to hang on at the bottom of the swing is twice the preformer's weight."

*I tried to attach a picture. Its not very good though, because I had to draw it*

I don't know how to approach the question but, my first question would be where is angle theta_i ?
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PhanthomJay
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Nov6-06, 07:18 PM
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Quote Quote by mirandasatterley
Any help with the following question would be appreciated. Please keep in mind that i'm not very good with physics.

"A circus trapeze consists of a bar suspended by two parallel ropes, each of length l, allowing performers to swing in a vertical circular arc. Suppose a performer with a mass m holds the bar and steps off an elevated platform, starting from rest with the ropes at an angle theta_i with respect to the vertical. Suppose the size of the performer's body is small compared to the length l, she does not pump the trapeze to swing higher, and air resistance is negigable.
A) Show that when the ropes make an angle theta with the vertical, the preformer must exert a force: mg(3 cos theta - 2 cos theta_1), so as to hang on.
B) Determine the angle theta_i for which the force needed to hang on at the bottom of the swing is twice the preformer's weight."

*I tried to attach a picture. Its not very good though, because I had to draw it*

I don't know how to approach the question but, my first question would be where is angle theta_i ?
You posted this somewhere yesterday I think, and I tried to give you a couple of hints. The angle theta is somewhere in between beta and -beta. It is a 'given' in part a, and you've got to find it in part b. Maybe someone else will help because I'm not giving any more hints. If you're a beginner at centripetal force and conservation of energy equations, this is not the problem you want to tackle first.


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