Difficult time with motion graphs & dynamics

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SUMMARY

The discussion focuses on calculating the force exerted by a chin-up bar on a person weighing 72.7 kg during a vertical motion. The participant initially miscalculated the acceleration as -60 m/s², leading to an incorrect tension force calculation using the formula F = ma. Upon realizing the acceleration was mistakenly noted in cm/s instead of m/s, the participant corrected their approach, emphasizing the importance of unit consistency in physics calculations.

PREREQUISITES
  • Understanding of Newton's Second Law (F = ma)
  • Knowledge of unit conversions (cm/s to m/s)
  • Basic principles of dynamics and motion graphs
  • Familiarity with tension forces in vertical motion scenarios
NEXT STEPS
  • Study unit conversion techniques in physics
  • Learn about dynamics involving tension forces in vertical motion
  • Explore advanced applications of Newton's laws in real-world scenarios
  • Review motion graphs and their interpretations in physics problems
USEFUL FOR

Students studying physics, particularly those focusing on dynamics and motion analysis, as well as educators looking for examples of common calculation errors in force and acceleration 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)
 

Attachments

  • upload_2018-10-8_15-29-4.png
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  • 5-p-041.gif
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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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