Saving Lives Through Seat Belts & Air Bags

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Homework Help Overview

The discussion revolves around the physics of automobile safety features, specifically seat belts and air bags, and their role in reducing forces during collisions. The problem involves calculating forces experienced by a person in a car crash under different conditions of restraint.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to determine the acceleration of a person in a collision based on given distances and initial velocity. There are questions about the calculations of force using mass and acceleration.

Discussion Status

Some participants have calculated accelerations and are discussing the resulting forces. There is uncertainty regarding the correctness of their answers, particularly in relation to significant figures and the feedback from the system being used for submission.

Contextual Notes

Participants mention using WebAssign for problem submission, which may have specific requirements for input formatting or significant figures.

aligass2004
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Homework Statement


Seat belts and air bags save lives by reducing the forces exerted on the driver and passengers in an automobile collision. Cars are designed with a "crumple zone" in the front of the car. In the even of an impact, the passenger compartment decelerates over a distance of about 1m as the front of the car crumples. An occupant restrained by seat belts and air bags decelerates with the car. By contrast, an unrestrained occupant keeps moving forward with no loss of speed until hitting the dashboard or windshield. These are unyielding surfaces, and the unfortunate occupant then decelerates over a distance of only about 5mm. a.) A 60 kg person is in a head-on collision. The car's speed at impact is 11m/s. Estimate the net force on the person if he or she is wearing a seat belt and if the air bag deploys. b.)Estimate the net force that ultimately stops the person if he or she is not restrained by a seat belt or air bag. c.) How do these forces compare to the person's weight? (They want to know F(a)/W = ? and F(b)/W = ?)


Homework Equations


F=ma


The Attempt at a Solution


I don't even know where to begin with this problem. I sat and read it a couple of times, and just had no idea where to begin.
 
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The main part of the problem is to find the acceleration... for the first case initial velocity is 11m/s... he comes to a stop over 1m... what is the acceleration?

second case again initial velocity is 11m/s... he comes to a stop over 5mm... what is the accleeration?

force is just mass times acceleration.
 
Having problems finding the acceleration. I got -60.5.
 
aligass2004 said:
Having problems finding the acceleration. I got -60.5.

Yes, that's correct. So what's the force?
 
The force would be 3630N? I put that, and it said it was wrong.
 
aligass2004 said:
The force would be 3630N? I put that, and it said it was wrong.

Hmmm... maybe -3630N ? I'm not sure...
 
Nope, I tried that too.
 
aligass2004 said:
Nope, I tried that too.

I don't understand why it isn't accepting the answer... Is the system sensitive about significant figures?
 
I don't think it is. We use WebAssign.
 

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