Solving the Car Crash Puzzle: Newtons 2nd Law

[denzel]

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.

 

[PeroK]

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.

 

[denzel]

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

I know the Kinematic Equations and how they work.

 

[PeroK]

I know the Kinematic Equations and how they work.

Then you can apply them here!

 

[denzel]

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?

 

[PeroK]

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?

 

[denzel]

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?

 

[PeroK]

So that 0.7 can be taken as the distance?

Yes.

 

[denzel]

Yes.

Thanks a lot!

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

 

[PeroK]

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.

 

[denzel]

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?

 

[PeroK]

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.

 

[denzel]

That question doesn't make a lot of sense.

Can you please show me the formulas I'm suppose to be taking into account?

 

[PeroK]

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: $a = \frac{\Delta v}{\Delta t}$.

 

[denzel]

V = d/t

then

a = v/t

I think I got it?