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![[Post New]](/templates/default/images/icon_minipost_new.gif) 23 Mar 2008 17:23:57 IST
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A solid cylinder of mass m and radius r is rolling on a rough plane of angle theta.The coeficcient of friction between cylinder and incline is  .Then(more than 1 can be correct)
a)friction force is always  mgcostheta
b)friction is dissipative force
c)by decreasing theta frictional force decreases
d)friction opposes translation and supports rotation
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23 Mar 2008 17:25:52 IST
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a and d i think
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23 Mar 2008 17:27:02 IST
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a)c)d)?
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23 Mar 2008 17:28:34 IST
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i think only c,d.
b) can be..
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23 Mar 2008 17:31:36 IST
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I think a,d
answer given c,d
xplain
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<TABLE CELLSPACING="1" CELLPADDING="1" BORDER="0">
<TR><TD>
Anyone who has never made a mistake has never tried anything new
You can never solve a problem on the level on which it was created.
When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That's relativity
Purpose of solving a problem is not simply to get the answer(the answer is only an evidence) but to develop your thinking ability |
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23 Mar 2008 17:33:05 IST
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When u decreas theta,the slope becomes less,so tendency to fall down also decreases and so fric. force also decreases...Friction opposes translation as u noe and it supports rotation by providing torque..
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23 Mar 2008 17:34:08 IST
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when we decrease  cos increases so frictional force always increases c cannot be true
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23 Mar 2008 17:34:16 IST
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Hey all, since the body is rolling, friction opposes rotation hence the ans shud be (a) ,(c) although the a option hasnt appeared clearly on my comp. rate if correct and correct if wrong cheers!!!
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23 Mar 2008 17:36:37 IST
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lampard how can frictional force decrease when cos is increasing
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23 Mar 2008 17:39:20 IST
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only c and d
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23 Mar 2008 17:42:08 IST
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but the frictional force will increase on decreasing |
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23 Mar 2008 17:42:55 IST
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frictional force=gsin /1+MR2/I
f sin
so frictional force decreases on decreasing angle of inclination
and frictional force provides a torque in the direction of angular velocity (abt COM) and hence
increases angular velocity
friction decr. linear velocity as it acts up the plane
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23 Mar 2008 17:44:10 IST
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it is acase of pure rolling f always acts up the incline so f comes to be f=mgsin /1+(mR 2/I) (I=moment of inertia) so f is proportional to sin so it will be c,d
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23 Mar 2008 17:44:23 IST
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a) is not true as it fails in a non inertial frame. Moreover, frictional force is not mgcos@ always. who said it is? It depends on the choice of the reference axes. The right explanation is given by Lampard
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Will nip in at times to solve problems :)
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23 Mar 2008 17:45:25 IST
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