What Causes Discrepancies in Calculating Shearing Stress in a Circular Shaft?

AI Thread Summary
The discussion centers on calculating the maximum shearing stress in a circular shaft subjected to torque. The original calculation yielded an incorrect result due to a failure to convert torque from foot-pounds to inch-pounds. The correct formula for shearing stress is applied, but the unit conversion is crucial for accurate results. After realizing the mistake, the user successfully recalculated the shearing stress, achieving the expected value of 17.39 ksi. Proper unit conversion is essential in engineering calculations to avoid discrepancies.
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Hey guys, I got a problem that goes like: A shaft with a circular cross section is subjected to a torque of 120ft-lb. Its shaft's diameter is 0.750 in and its length is 15 in., determine the maximum shearing stress.

I did the following: I tried to use shearing stress = Tr/J in which i plugged in as followed (120*.750/2)/(pi/32)*.750^4 and i get 1448, but the answer should be17.39ksi. I assume i am not getting the right answer because I am not factoring in the length but I am not sure. Any help is appreciated, thanks
 
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nm, i figured it out, Stupid me forgot to convert the ft-lb to inch-lb.
 

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