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23 Feb 2007 18:47:50 IST

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693

plzzz help-rotation prob

None

h.c verma
rotational mech

objective II
Q-11
Q-15

Q-11-

A sphere cannot roll on-

a)a smooth horizontal surface
b)a smooth inclined surface

plzz help...

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Comments (8)

ankur khurana

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23 Feb 2007 18:58:31 IST

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smooth horizontal plane and inclined plane don't have any friction so no torque is there to provide rolling .So they can only slip not roll.

anubhav07

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23 Feb 2007 19:42:43 IST

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well i think ur ans is wrong....check h.c verma

on a horizontal surface when a sphere starts pure rolling the friction vanishes...isn't it...experts plzz reply!!!

anubhav07

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23 Feb 2007 19:45:49 IST

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also...After a sphere starts rolling dosen't the lowermost pt has a tendency to move in the backward/forward direction??plzz reply somebody

joy francis

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23 Feb 2007 20:57:58 IST

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pure rolling means that the lowermost point is having zero velocity, zero momentum, zero force, zero torque.

the torque of friction about the lowermost point is always zero.

so, we are left with the torque due to gravity, which can only be zero on a horizontal surface. not on an incline, since r cannot be zero on the incline.

vishak p

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23 Feb 2007 21:00:34 IST

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on a smooth horizontal surface, as a constant force = mg sin x is being applied to the body, to balance whose sliding effect there is no frictional force.in the latter case, u do need a frictional force as no external force is acting on the sphere !!

Bipin Dubey

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Joined: 23 Jan 2007

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26 Feb 2007 12:01:13 IST

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Friction is necessary for rolling whatever be the surface horizontal or inclined.Friction provides the necessary torque for rolling.

Anubhav, friction does not vanish on pure rolling. Its work done is zero in pure rolling since there is no displacement at the point of friction force acting.

Best Wishes

vishak p

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26 Feb 2007 12:09:36 IST

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BIPIN SIR

I REQUEST U TO PLEASE take a little time for my question of electric field in the expert panel as i am stuck badly and unable to move forward !

rishiraj jaiwal

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26 Feb 2007 14:41:14 IST

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A body can roll on a frictionless horizontal surface only if it enters that region while already in rolling condition. As there will be no horizontal force, its angular velocity and linear velocity will remain same; i.e. rolling condition will prevail throughout.

But no body can roll on a frictionless incline plane, if left alone, i.e. in effect of gravity alone, although it may be purely rolling earlier. This will be so; as component of mg parellel to incline will tend to change the linear speed but there will be no torque to change the angular vel. in accord with the rolling condition.

Rishiraj

B.Tech. from ITBHU

Chemical engg. & Technology

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