Difficult time with motion graphs & dynamics

AI Thread Summary
The discussion focuses on solving a physics problem involving motion graphs and dynamics related to a chin-up exercise. The user initially calculated the acceleration at 1.6 seconds as -60 m/s² and attempted to apply Newton's second law to find the force exerted by the chin-up bar. However, they later realized that their acceleration value was incorrectly converted from cm/s to m/s, which led to an erroneous force calculation. This highlights the importance of unit conversion in physics problems. The user corrected their mistake, indicating a learning moment in the process of solving dynamics problems.
devilish_wit
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Homework Statement


The figure below shows the speed of a person's body as he does a chin-up. Assume the motion is vertical and the mass of the person's body is 72.7 kg. Determine the force exerted by the chin-up bar on his body at the following times.

5-p-041.gif


My answers:

upload_2018-10-8_15-29-4.png

Homework Equations


F = ma

The Attempt at a Solution


I'm not quite sure how to solve that last part:

I solved for the acceleration at 1.6s which is -60m/s^2.

F = ma
-mg + T = m a
T = 72.7kg(60m/s^2) + (9.8m/s^2)(72.7kg)
T = 3649.54?? (this one's wrong)
 

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Physics news on Phys.org
oh never mind guys, I realized I made a stupid mistake. My acceleration was in cm/s and not in m/s!
 

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