Forces and defining coordinate systems

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SUMMARY

The discussion focuses on defining coordinate systems in physics, specifically setting upward as the positive y-direction. The participant calculates the acceleration using the formula a=(Vf-Vi)/t, resulting in +156 ft/s². They clarify that the weight (w=mg) acts downward, leading to the equation ƩF = T - w. The confusion regarding units arises from the use of pounds and Newtons, with the participant suggesting that the mention of Newtons may be a typographical error.

PREREQUISITES
  • Understanding of Newton's Second Law (F=ma)
  • Familiarity with coordinate systems in physics
  • Knowledge of unit conversions between pounds and Newtons
  • Basic grasp of kinematic equations
NEXT STEPS
  • Study the implications of different coordinate systems in physics
  • Learn about unit conversions between imperial and metric systems
  • Explore the concept of weight and mass, specifically in the context of slugs and pounds
  • Investigate kinematic equations and their applications in various scenarios
USEFUL FOR

Students studying physics, educators teaching coordinate systems, and anyone interested in understanding the application of forces in motion.

Amideus
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Homework Statement


parachute.jpg



Homework Equations


F=ma
vi=vf + at


The Attempt at a Solution


If i was to define upward as positive y direction, would the answer be = -881 pounds (btw why is the answer in the image in Newtons?) and because i defined upward as +y would
ƩF = T - w? where w = mg.
 
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I think you are right about the units. I am not too familiar with slugs, pounds, ft/s^2 but I think you're right about Newtons being a typo.

On the other hand, you are wrong about the direction of the force. Since we set upward as positive, the initial and final velocities are negative.

a=(Vf-Vi)/t=(-35-(160))/0.80=+156 ft/s^2

Since the acceleration is upward, the retarding force is also upward.
 

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