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Old May 11th 2012, 08:17 PM   #1
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Exclamation Circular motion explanation needed!

http://www.xtremepapers.com/papers/C...2_w07_qp_4.pdf

Q1b(ii) I have no idea how to find L. Please help!


http://www.xtremepapers.com/papers/C...2_w08_qp_4.pdf

Q1b(i) Please explain to me. Is R getting smaller? Why normal reaction is 0 at the poles?


Appreciate all the help!
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Old May 20th 2012, 11:09 PM   #2
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For the first question,

Use the hook's law, F=kx

apply it to the static scenario

F=5N, x=14.8-13=1.8cm then,

5=1.8k => k=5/1.8 N/cm

now lets consider the dynamic motion and apply newton's second law to the mass which is below the point C

F_s-W=ma where F_s is force by the string and W is the weight

kl-mg=mrw^2

isolate l which is the extended length of the string,

l=m(rw^2+g)/k w is found in the part i
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Old May 20th 2012, 11:16 PM   #3
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for the second question,

The normal reaction will not be equal to zero.

at the equator, the gravitational force and the normal reaction together will effect the centripetal force. But at the pole since m is not rotating it does not need a centripetal force. Thus the normal reaction and its gravitational force should cancel each other
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