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Determine the magnitude of the torque

  • Thread starter deltas
  • Start date
  • #1
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Homework Statement


A 25.0 N weight is held in the outstretched hand of a person with a shoulder-to-elbow length of 26.0 cm and an elbow-to-wrist length of 22.5 cm. The center of the weight is 7.5 cm from the person's wrist. A) Determine the magnitude of the torque about the elbow produced by the weight and B) Determine the magnitude of the torque about the shoulder produced by the weight.

http://educog.com/res/fsu/capalibrary/24equilibrium/Graphics/prob22a.gif​
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Homework Equations


Well, I can think of a few ways to solve for torque:

t = lF
tnet = I[tex]\alpha[/tex]
tnet = I[tex]\alpha[/tex]
(I = mr2)
(F = ma)

The Attempt at a Solution


Alright, well, for the first equation I knew that t = lF, where l is the lever arm distance and F is the force in newtons.
l = 30.1 (a), 56.1(b)
F = ma
F = 2.55 x 9.81 = 25 (given)
t = 25 x 30.1 [56.1]
t = 752.5 NM [1403 NM]
Something is clearly not right here, help! I can tell I'm missing something basic, but I don't know what.
 
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Answers and Replies

  • #2
ideasrule
Homework Helper
2,266
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Check your units.
 
  • #3
7
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Centimeters? Was it centimeters the whole time?
 
  • #4
ideasrule
Homework Helper
2,266
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It wasn't because you used Nm for the torque when it should be N*cm.
 
  • #5
7
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No, that's what I meant. I hadn't noticed that it was cm instead of m! Thank you!
 

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