# Solving the Car Crash Puzzle: Newtons 2nd Law

• denzel
In summary: I do that, how do I differentiate between average and constant velocity?I think I got it?If you are using average velocity, then you would use the following equation: ##v = \frac{a}{t}##.If you are using average velocity, then you would use the following equation: ##v = \frac{a}{t}##.
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.

## 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.

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.

## 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?

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.

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?

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.

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?

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}##.

V = d/t

then

a = v/t

I think I got it?

## 1. What is Newton's 2nd Law of Motion?

Newton's 2nd Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. In simpler terms, the greater the force exerted on an object, the more it will accelerate, and the heavier the object, the less it will accelerate.

## 2. How does Newton's 2nd Law apply to car crashes?

In a car crash, the force of the impact causes the car to decelerate rapidly. According to Newton's 2nd Law, this deceleration is directly proportional to the force of the impact and inversely proportional to the mass of the car. This means that the higher the force of the impact, the greater the deceleration and the more damage that will occur to the car and its occupants.

## 3. What factors affect the force of impact in a car crash?

The force of impact in a car crash is affected by several factors, including the speed of the car, the mass of the car, and the stiffness of the objects involved in the collision. The angle and direction of the impact can also affect the force.

## 4. How can we reduce the force of impact in a car crash?

To reduce the force of impact in a car crash, we can focus on two main factors: reducing the speed of the car and increasing the time it takes for the car to come to a stop. This can be achieved through measures such as wearing seatbelts, using airbags, and designing cars with crumple zones that absorb some of the force of impact.

## 5. How can Newton's 2nd Law help us understand and prevent car crashes?

By understanding Newton's 2nd Law, we can see how the force of impact in a car crash is directly related to the speed and mass of the car. This knowledge can inform safety measures and car design to help prevent or minimize the damage and injuries caused by car crashes. Additionally, it can also help us understand the importance of obeying speed limits and maintaining safe driving practices to reduce the likelihood of a car crash occurring.

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