Hanging Rod - Torque Question

  • Thread starter Joosh
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  • #1
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Hey, folks! So upon studying for my Physics final tomorrow, I came across this question on the practice exam, which I know the answer is D from the solution key. However, I'm not sure how to get that for the answer.

1. Homework Statement

iNmDGIX.jpg


Homework Equations


τ = rA × Fnet
LA = Ltrans, A + Lrot
Ltrans = rcm × Ptot
Lrot = r1 × p1 + r2 × p2 + ...

The Attempt at a Solution


I personally don't entirely know where to start. I'm going to guess this is a torque-related question, but I'm not sure if that's the right way to go at it.
 

Answers and Replies

  • #2
PhanthomJay
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The rod is at rest when the force F is applied. What can you say about what the sum of the torques about the hinge must be for bodies at rest? No need to get involved with momentum
 
  • #3
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The net torque would equal zero.
 
  • #4
haruspex
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The net torque would equal zero.
So what are the torques? What equation do you get for a zero sum?
 
  • #5
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Would it just be gravity and the force pushing the rod upwards?
 
  • #6
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I asked one of the graduate teaching assistants about this and he was able to help me figure this out. I simply forgot that the center of mass is where gravity is pulling down on the rod.
 

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