Solving the Car Crash Puzzle: Newtons 2nd Law

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Homework Help Overview

The discussion revolves around a physics problem involving a car crash scenario, where a car collides with an immovable wall. The problem requires calculating the acceleration during the deformation of the car's crush zone and the time interval for this compression, as well as considerations for the airbag system and spring constant. The subject area primarily involves Newton's second law and kinematics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of Newton's second law and kinematic equations to the problem. They explore the relationship between initial velocity, stopping distance, and acceleration. Questions arise regarding the assumptions of constant velocity versus average velocity and the implications of the car still being in motion.

Discussion Status

The discussion is ongoing, with participants attempting to clarify their understanding of the problem and the relevant physics concepts. Some guidance has been offered regarding the use of kinematic equations and the need to consider the final velocity in the context of the problem.

Contextual Notes

Participants express uncertainty about the basic principles involved and the constraints of the problem, such as the assumption of uniform acceleration and the implications of the car's motion during the collision.

denzel
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I've been trying to study for my final and I can't seem to figure out how is this suppose to work.

1. Homework Statement
A wall (m infinite, v=0) hits a car (m=2600 kg; v=142 km/h). The car becomes deformed and the crush zone (0.7 m) is compressed. Calculate the corresponding acceleration (assuming a constant value). Within which time interval does that compression happen? Try to find out, how fast each part of the airbag system therefore has to operate. Imagine the crush-zone is replaced by a spring. Calculate the required spring constant.

Homework Equations

The Attempt at a Solution


I think it has to do with Newtons second law but I don't know what to do with that velocity.
 
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denzel said:
I've been trying to study for my final and I can't seem to figure out how is this suppose to work.

1. Homework Statement
A wall (m infinite, v=0) hits a car (m=2600 kg; v=142 km/h). The car becomes deformed and the crush zone (0.7 m) is compressed. Calculate the corresponding acceleration (assuming a constant value). Within which time interval does that compression happen? Try to find out, how fast each part of the airbag system therefore has to operate. Imagine the crush-zone is replaced by a spring. Calculate the required spring constant.

Homework Equations

The Attempt at a Solution


I think it has to do with Newtons second law but I don't know what to do with that velocity.

What else do you know about kinematics? Netwon's second law is a start.
 
PeroK said:
What else do you know about kinematics? Netwon's second law is a start.

I know the Kinematic Equations and how they work.
 
denzel said:
I know the Kinematic Equations and how they work.

Then you can apply them here!
 
PeroK said:
Then you can apply them here!

Can you give me a hint? I know that I'm over looking something very basic but I can't seem to find what?
 
denzel said:
Can you give me a hint? I know that I'm over looking something very basic but I can't seem to find what?

Car - initial velocity given - uniform acceleration assumed - stopping distance given - find force and stopping time.

That's the problem in a nutshell, isn't it?
 
PeroK said:
Car - initial velocity given - uniform acceleration assumed - stopping distance given - find force and stopping time.

That's the problem in a nutshell, isn't it?

So that 0.7 can be taken as the distance?
 
denzel said:
So that 0.7 can be taken as the distance?

Yes.
 
PeroK said:
Yes.
Thanks a lot!

So I should assume that the final velocity is 0 and use the kinematic equation to get acceleration?
 
  • #10
denzel said:
Thanks a lot!

So I should assume that the final velocity is 0 and use the kinematic equation to get acceleration?

You need to think on your feet more. If the car is still moving, then you know too little to solve the problem.
 
  • #11
PeroK said:
You need to think on your feet more. If the car is still moving, then you know too little to solve the problem.
I'm at a loss again then, is average velocity the same as a constant velocity?
 
  • #12
denzel said:
I'm at a loss again then, is average velocity the same as a constant velocity?

That question doesn't make a lot of sense.
 
  • #13
PeroK said:
That question doesn't make a lot of sense.
Can you please show me the formulas I'm suppose to be taking into account?
 
  • #14
denzel said:
Can you please show me the formulas I'm suppose to be taking into account?

We can only help so much. We can't teach you physics from the beginning. One formula you might like to consider, for constant acceleration is: ##a = \frac{\Delta v}{\Delta t}##.
 
  • #15
V = d/t

then

a = v/t

I think I got it?
 

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