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posted by  Definitive1 on 11/4/2009 10:14:28 PM  |  status: Closed  |  Earned Karma: 54

circular motion and forces

Course Textbook Chapter Problem Needs by
Calculus Based Physics Physics for Scientists and Engineers 7th by Serway, Jewett 6 N/A 11/5/2009 at 12:00:00 PM
Question Details:
A 600 gram mass connected to a string is being whirled in a vertical circle with a 0.8 meter radius at a constant speed.
a) Show free body diagram when it is at the top of it's motion.  Label all forces.
b) Determine the speed if the tension in the string is twice the weight of the mass.
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posted by jacksparrow on 11/4/2009 10:35:18 PM  |  status: Live
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Response Details:


There is a centripetal force going to the center, and gravity.

T = 2 * weight
T = 2 * (g * mass)
T = 2 * 9.81 & 0.6
T = 11.77N

centripetal force = m v2
                                   r
Force = .6 v2
                  r

11.77 = .6 v2
                 0.8
v = 3.96 m/s
(SME)
posted by christina.S on 11/4/2009 10:51:20 PM  |  status: Live
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Response Details:
 
                      
.
Free body diagram is as shown above .
.
Vtop    =  √gR   =  √9.8 * 0.8   =  2.8  m /s
.
Vbottom  =  √5gR =  √5 *9.8 *0.8   =  6.26  m /s
.
Tention at top is :   Ttop  =  m Vtop2  /  r       +   mg   =  ------  N
.
                             Tbottom  =  m Vbottom2  /  r      -   mg   =  ------  N 
.
Using  Ttop    ,  Tbottom   calculate   velocity  if tention is doubled .
.
Hope this helps u!
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posted by Definitive1 on 11/4/2009 11:26:08 PM  |  status: Live
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Response Details:
Thanks!
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