Newtonian - Force, Gravity, and Bungee Jumping

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Homework Help Overview

The problem involves a bungee jumping scenario where a person weighing 55 kg jumps off a bridge, and the objective is to determine the force exerted by the bungee cord when the acceleration is 7.8 m/s² downward. The context includes gravitational force and the forces acting on the jumper.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of forces, particularly questioning the rationale behind subtracting the forces involved. There is an exploration of the forces acting on the jumper, including gravitational force and the force exerted by the bungee cord.

Discussion Status

Some participants are seeking clarification on the reasoning for the subtraction of forces, indicating a productive dialogue about the underlying physics concepts. The discussion is ongoing, with attempts to clarify the calculations and assumptions made by the original poster.

Contextual Notes

There is a mention of the original poster's grid setup and the potential confusion regarding the direction of forces and accelerations. The discussion reflects on the definitions and interpretations of the forces involved in the scenario.

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Homework Statement


A person weighing 55kg jumps off of a bridge with a bungee cord attached. The problem seeks to find the bungee cords Force vector when the acceleration is 7.8m/s2 in the downward direction.

m = 55kg
a1 = g = 9.8m/s2

To find:
F1 when a2 = 7.8m/s2 downward.

I've specified my grid as [tex]\uparrow[/tex]+ [tex]\rightarrow[/tex]+ so the accelerations are technically negative.

Homework Equations


[tex]\Sigma[/tex]F = ma


The Attempt at a Solution


[tex]\Sigma[/tex]F = ma
[tex]\Sigma[/tex]F=55kg(-7.8m/s2)
[tex]\Sigma[/tex]F = -418N

[tex]\Sigma[/tex]F = F1 - F2
[tex]\Sigma[/tex]F = 539N - 418N
Force of bungee cord acting = +121N
 
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Why did you subtract the forces?
 
semc said:
Why did you subtract the forces?

The 539N was the Force with F=ma and a = g. I think I forgot to write that.
The -428N was the Force with F=ma and a = 7.8m/s2.

My inclination was to subtract the forces to get the force required by the bungee cord to slow the decent to the 7.8m/s2
 
Well since gravitational force is downwards and he is traveling downwards...
 

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