Determine the magnitude of the torque

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AI Thread Summary
The discussion focuses on calculating the torque produced by a 25.0 N weight held in an outstretched hand, with specific measurements for the shoulder-to-elbow and elbow-to-wrist lengths. The participant attempts to use the torque formula t = lF but encounters confusion regarding the units, mistakenly using meters instead of centimeters. After recalculating, they realize the need to convert the lever arm distances to the correct units for accurate torque measurement. The correct torque values are determined to be 752.5 N·cm about the elbow and 1403 N·cm about the shoulder. The conversation emphasizes the importance of unit consistency in physics calculations.
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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\alpha
tnet = I\alpha
(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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Check your units.
 


Centimeters? Was it centimeters the whole time?
 


It wasn't because you used Nm for the torque when it should be N*cm.
 


No, that's what I meant. I hadn't noticed that it was cm instead of m! Thank you!
 

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