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Blazing goIITian

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21 Dec 2007 17:10:34 IST

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Direction of friction - small challenge

None

Tell me the direction of friction at the topmost and at the bottommost point with proper explanation. The correct reply will get a salute, else I'll post the answer by today night. Its a simple one, no calculations involved.

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A K

Cool goIITian

Joined: 21 Dec 2007

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21 Dec 2007 17:28:12 IST

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Direction of friction - small challenge

abc xyz

Blazing goIITian

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21 Dec 2007 18:06:57 IST

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at A it should be backward.

coz string is stationary, while the body is rotating clockwise (or relative motion is forward).

at B it should be forward.
coz the relative of the body is backward.

hope its right.

Karthik M

Blazing goIITian

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21 Dec 2007 18:08:24 IST

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wrong

'',' Off to a nu start!!

Blazing goIITian

Joined: 13 Jan 2007

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21 Dec 2007 18:42:09 IST

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yes....att B it will be in backward direction direction.as FRICTION OPPOSES RELATIVE ROLLING.

at A i am not sure but will go for backward direction..may be the same reason which i gave above

AYUSHITANDON

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21 Dec 2007 18:43:53 IST

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forward at a and b both

Learner .

Blazing goIITian

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21 Dec 2007 18:55:05 IST

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Wow!We've all given diff answers...here's mine:

As I see it,B lies on the ground..motion of circle relative to ground is forward..

so friction should be backwards.

At A,which is on the body,the string is trying to pull it forward,so the body will try to resist this change.

Hence,again,friction will be to the back

abhishek sinha

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21 Dec 2007 19:00:25 IST

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in forward direction at both points . Its friction that is causing motion

Karthik M

Blazing goIITian

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21 Dec 2007 19:01:43 IST

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Feymann is correct!!! Take a salute

'',' Off to a nu start!!

Blazing goIITian

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21 Dec 2007 19:01:54 IST

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no.its force F which is causing rolling..

Karthik M

Blazing goIITian

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21 Dec 2007 19:04:21 IST

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Though I would say his explanation is not very elaborate, ie, not to the point

abhishek sinha

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21 Dec 2007 19:05:11 IST

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try to draw the FBD for both the rope and wheel . Soln will be clear

Learner .

Blazing goIITian

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21 Dec 2007 19:19:57 IST

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Ahh...I get it for B-the point will move opposite direction of friction..

But I'm unable to explain it for A..could you elucidate please?

abhishek sinha

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21 Dec 2007 19:28:14 IST

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For A consider the forces acting on rope ;one is F in the forward direction & other is the friction . For equlibrium of rope friction on rope must be backwards .Again from third law friction on wheel must be in the forward direction ( they are action - reaction pairs) . Clear enough ?

Learner .

Blazing goIITian

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21 Dec 2007 19:31:24 IST

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Yes.Thanks a lot!

'',' Off to a nu start!!

Blazing goIITian

Joined: 13 Jan 2007

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22 Dec 2007 13:57:09 IST

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yes...u r right guys..i interpret thw directions wrong...i took the forward dircn. as backward 1 & vice-versa. and this happens only when ur mind needs rest...sorryyy...u r right.

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