Physics Help Forum tension problem..

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Oct 27th 2009, 05:36 PM #1 Senior Member   Join Date: Sep 2009 Location: St. John's, NL Posts: 124 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?
 Oct 27th 2009, 11:42 PM #2 Senior Member   Join Date: Oct 2009 Location: india Posts: 409 how about doing free body diagram at lowest point? T(UP)-mg(down)=mv^2/r gives T=146 N.
 Oct 28th 2009, 02:59 AM #3 Physics Team   Join Date: Feb 2009 Posts: 1,425 And the accln should be v^2/r . Last edited by physicsquest; Oct 29th 2009 at 11:34 PM. Reason: wrong accln corrected
 Oct 28th 2009, 08:09 AM #4 Senior Member   Join Date: Oct 2009 Location: india Posts: 409 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.
 Oct 29th 2009, 11:33 PM #5 Physics Team   Join Date: Feb 2009 Posts: 1,425 Thanks. You are right. I will modify my previous post
 Oct 30th 2009, 09:38 PM #6 Banned   Join Date: Aug 2009 Location: UK Posts: 240 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 10:17 PM.
 Oct 30th 2009, 10:30 PM #7 Senior Member   Join Date: Oct 2009 Location: india Posts: 409 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.
 Oct 30th 2009, 10:35 PM #8 Banned   Join Date: Aug 2009 Location: UK Posts: 240 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.
 Oct 30th 2009, 10:39 PM #9 Member   Join Date: Oct 2009 Posts: 58 I just want to provide something : Why dont you warn christina !
 Oct 30th 2009, 10:40 PM #10 Banned   Join Date: Aug 2009 Location: UK Posts: 240 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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