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Mechanics

New kid on the Block

 Joined: 16 Mar 2012 Post: 1
16 Mar 2012 19:04:03 IST
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RIGID BODY DYNAMICS
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in any general problem of rigid body dynamics involving a pulley(when not considered light and has some inertia),we consider the tension on both the sides of ideal string to be different.....but when the string is ideal,it is considered to be massless,meaning thereby no gravitational force on it and no normal rkn force to the pulley....When the normal rkn force is zero,no frictional  force should  exist ....then how can tension be different????

Scorching goIITian

Joined: 10 Feb 2012
Posts: 262
17 Mar 2012 14:55:24 IST
1 people liked this

It's not that way. According to the problem we know that for the blocks to move the pulley should rotate. Since the pulley is mass less there should be some external torque it should have to rotate. First just assume the tension to be equal and calculate the net torque you find that the pulley experiences zero torque i.e it won't rotate. now you are clear that the tension should be different. hoping you understand.If yes please like..

Forum Expert
Joined: 21 Jun 2011
Posts: 743
29 Mar 2012 21:14:13 IST
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just as said above , if the difference in tension occurs due to a nodal point , that is the pulley ... if there is no tension difference that means the mass at either side of the pulley is equal , hence no rotation of the pulley is possible

Forum Expert
Joined: 21 Jun 2011
Posts: 743
29 Mar 2012 21:14:47 IST
0 people liked this

just as said above , if the difference in tension occurs due to a nodal point , that is the pulley ... if there is no tension difference that means the mass at either side of the pulley is equal , hence no rotation of the pulley is possible

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