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Easy rotational problem

  • Thread starter Sheneron
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  • #1
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[SOLVED] Easy rotational problem

Homework Statement


A string is wound around a uniform disk of radius 0.25m and mass 8.00kg. The end of the string is pulled with a constant force of 50.0 N, and there is a frictional torque acting at the axle of 3.00 Nm.
A) Find the total torque exerted on the disk

The Attempt at a Solution


I think I have it solved... just wanted to make sure and I have one question. It says that the frictional torque is acting on the axle, do I still use the radius r=0.25 to find the torque for that part? Here is what I did:

[tex]\Sigma \tau = \Sigma Fd[/tex]
[tex]\Sigma \tau = (50)(0.25) + (-3)(0.25)[/tex]
[tex]\Sigma \tau = 11.75 Nm [/tex]

So is that how I would find the net torque?
 

Answers and Replies

  • #2
Doc Al
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It says that the frictional torque is acting on the axle, do I still use the radius r=0.25 to find the torque for that part?
Careful. For friction they gave you the torque, not the force. So you don't have to use any radius to find the frictional torque.
 
  • #3
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Oh yeah I just realized that. so I guess what i meant to say would the net force end up being 9.5 Nm?
 
  • #4
Doc Al
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so I guess what i meant to say would the net force end up being 9.5 Nm?
The net torque is 9.5 Nm.
 
  • #5
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oops again...
Thanks.
 

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