Some basic questions about collision force

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    Collision Force
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Discussion Overview

The discussion revolves around the forces involved in collisions, specifically comparing the forces exerted by different masses during a collision and the calculation of forces based on initial conditions. It includes theoretical considerations, practical applications, and questions about the adequacy of provided information.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions how to reconcile Newton's 3rd law with the differing forces experienced by a small car and a big truck during a collision, seeking clarification on determining the force upon impact based on initial forces.
  • Another participant mentions that in inelastic collisions, total momentum is conserved, suggesting that the change in momentum divided by collision time can yield an average force, while noting that kinetic energy is not conserved in such collisions.
  • A participant queries whether the information provided for the second question is sufficient for analysis and seeks further clarification on the first question.
  • One participant introduces the concept of modern cars designed to absorb shock during collisions, implying a practical aspect of collision dynamics.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the adequacy of information for the questions posed, and there is no consensus on how to approach the calculations or the implications of Newton's laws in the context of the collisions discussed.

Contextual Notes

The discussion highlights potential limitations in the provided data, such as assumptions about final velocities and the nature of the collisions (elastic vs. inelastic), which may affect the calculations of forces.

Who May Find This Useful

This discussion may be useful for students studying physics, particularly those interested in collision dynamics, momentum, and force calculations in real-world scenarios.

12thString
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1. a small car and a big truck collided. as Newton's 3rd law states, they should apply the same amount of force with each other. so if the big truck has a mass of (just to make it simple) 5kg and acc of 2m/s to the right and the small car has a mass of 2kg and acc of 3m/s to the left. (Ftruck=+10N, Fcar=-6N) of course the car has a smaller force, but as stated above, upon collision, they should have the same force? how do i determine that force given their initial[?] forces. please clarify me on this. a follow up question would be that if given the initial forces acting on two known masses, how can i determine the force upon their impact?

2. I've read in a magazine that when 2 motorbikes collide, they'll produce roughly 124K N of energy. Given that their initial velocity is the same at 50mph (22.2m/s, one positive and one negative of course since this is just one dimensional collision) and their masses are 80 and 90kg with a collision time of 0.015s, i was wondrin with how they derived this 124K N of force. I can't use conservation of momentum (and F=m[tex]\Delta[/tex]v/[tex]\Delta[/tex]t also) since i can't assume that they have zero final velocity as that would mean that they have the same mass. how should i use the given variables?


please enlighten me guys. ^^
 
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In inelastic collisions, the total momentum is conserved, so the momentum before is equal to the momentum after. Then determine the change in momentum of each mass and divide by the time over which it occurs. That would given an averate force over that time period (collsion time).

http://hyperphysics.phy-astr.gsu.edu/hbase/inecol.html

In inelastic collisions, the kinetic energy is not conserved.
 
does that mean that the information provided in question number 2 is insufficient?

and how about question number 1?

thanks for the reply.
 
Last edited:
The cars made now are ones that absorb the shock for an instant, giving you time to react or buckle you feet and prepare for impact.
 

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