How Much Force is Needed to Jump?

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Homework Help Overview

The discussion revolves around determining the force required for a person to jump, specifically considering the acceleration during the jump and the effects of gravity. The subject area includes concepts from mechanics, particularly forces and motion.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the relationship between net acceleration and gravitational force, questioning whether gravity needs to be accounted for in their calculations. They discuss the distinction between net force and the normal force required to push off the ground.

Discussion Status

Participants are actively engaging with the problem, raising questions about the interpretation of the force needed to jump. Some suggest that the problem is asking for the normal force, while others are clarifying the role of net acceleration and gravity in their calculations. There is a productive exchange of ideas, but no explicit consensus has been reached.

Contextual Notes

The original question includes specific parameters such as jump height, time of ground contact, and mass, which are being analyzed to determine the necessary force. Participants are also considering the implications of these parameters on their calculations.

localrob
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If I wanted to know how much force is required to jump, and I know my acceleration while jumping, would I just use F=ma. Or do I need to account for gravity, as in use
Fjump - Fg = ma
 
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if the acc. you find is the net acc. then i guess you don't need to consider gravity as ots already considered while finding the net acc.
 
Yeah, that's what I was thinking.
Initially I was given the final velocity when jumping and the time in contact with the ground.
Vf = vi + at
That should be my net acceleration, because that is the actual acceleration needed to reach Vf.
 
If the question is what force do I need to push off the ground with, then aren't I looking for Fnormal and not net force?
The force that I push off the ground with is equal/opposite to the force normal acting on me.
So shouldn't I be solving FN - Fg = ma for FN?
 
please can you provide full question
 
Question:
If someone is able to jump 2.0 m into the air
a) How what speed must they leave the ground with?(ignore air resistance)
b) If they are in contact with the ground for 0.25 sec and have a mass of 65kg, what force must they push off the ground with?

Solution:
a) Going from the ground to max height
vi = ?, vf = 0m/s, a = -9.8m/s2, \Deltay = 2.0m
vf2 = vi2+2ay
vi = 6.26m/s

b) just for the jumping part
vi = 0m/s, vf = 6.26m/s, a = ?, t = 0.25
Find acceleration using vf=vi +at
a = 25.04 m;s2

Now, as you read the question, do you think it's asking for the net force applied to the person to jump or is it asking what the person must push off with?
 
net force acting on man must be now ma
this will include the gravity force and the normal reaction acting on him

localrob said:
Now, as you read the question, do you think it's asking for the net force applied to the person to jump or is it asking what the person must push off with?

I guess they are asking the force with which the man must push the ground, which is the normal rxn acting on it
 
cupid.callin said:
I guess they are asking the force with which the man must push the ground, which is the normal rxn acting on it

Yes I agree with you. I think they are asking for the normal force.
Thanks for the help.
 

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