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Old Oct 27th 2009, 04:36 PM   #1
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tension problem..

A steel ball of mass 1.23 kg is attached to a thin (massless) cable and whirled around in a circle in a vertical plane.The circle has a radius of 1.30 m. When it is at the bottom of the circle, the ball has a speed of 11.9 m/s. Calculate the magnitude of the tension in the cable when the mass is at the bottom of the circle.

Hint: Draw the free body diagram for the mass when it is at the bottom of the circle. Be careful with the directions of the forces acting on the ball. The NET force acting on the ball is related to the acceleration of the ball by Newton's second law. What is the acceleration of the ball when it is at the bottom of the circle?


what i did was:
F=mv^2/r
=1.23*(11.9)^2/1.30
=133.9N
thought this was an answer but its not.

Ac=v^2/r
=(11.9)^2/1.30
=108.9 m/s^2 (?)

how do i do this problem?
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Old Oct 27th 2009, 10:42 PM   #2
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how about doing free body diagram at lowest point?
T(UP)-mg(down)=mv^2/r gives T=146 N.
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Old Oct 28th 2009, 01:59 AM   #3
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And the accln should be v^2/r .

Last edited by physicsquest; Oct 29th 2009 at 10:34 PM. Reason: wrong accln corrected
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Old Oct 28th 2009, 07:09 AM   #4
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dear physicsquest, dont you think the acceleration should be just v^2/R, not (v^2/r - g)? because centripetal force is always the net force, not a separate one.
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Old Oct 29th 2009, 10:33 PM   #5
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Thanks. You are right. I will modify my previous post
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Old Oct 30th 2009, 08:38 PM   #6
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Guys read the forum rules please.





4) Do not try to hack the game arcade. People earned their high scores honestly it would be unfair for them if you cheat. Also, it’s embarrassing when you hack a free game arcade, seriously.


It really is embarrassing coming on here to watch r.samanta get false thanks just to pump his scores up, it really is sickly guys honestly, just remember this is a physics forum.

Christina has given out approx 44 thanks and r.samanta must of had 29 of them, who are you guys trying to fool? LOL!

Last edited by Paul46; Oct 30th 2009 at 09:17 PM.
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Old Oct 30th 2009, 09:30 PM   #7
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dear paul,
if u kindly look at the thread pre-exam problem, u will have a clear idea that i myself have expressed doubts in the sea of thanks that i received. i enjoy physics and like to help other students. i dont post to receive thanks. u can see that i have also thanked others,(including u) loads of times.your remarks have come as a shock to me, i must confess.
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Old Oct 30th 2009, 09:35 PM   #8
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It just seems strange how christina asks the questions and only you or physicsquest get to answer them and receive thanks, i've posted in several of these threads after you to only get ignored. The problem has been reported to admin by myself.
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Old Oct 30th 2009, 09:39 PM   #9
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I just want to provide something : Why dont you warn christina !
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Old Oct 30th 2009, 09:40 PM   #10
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Read this thread for instance, i even sent christina a private msg making her aware that i replied.

http://www.physicshelpforum.com/phys...n-problem.html
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