# Find the change in kinetic energy of the car

• hcps-chent1

## Homework Statement

A 2436 kg car has a speed of 10.7 m/s when it hits a tree. The tree doesn’t move and the
car comes to rest.
a) Find the change in kinetic energy of the car.
b) Find the amount of work done by the car as its front is pushed in.
c) Find the magnitude of the force that pushed the front of the car in by 54 cm.

## Homework Equations

Kinetic energy=1/2mass*speed^2

## The Attempt at a Solution

1/2*2436(10.7^2)=139449J of kinetic energy now what

## Homework Statement

A 2436 kg car has a speed of 10.7 m/s when it hits a tree. The tree doesn’t move and the
car comes to rest.
a) Find the change in kinetic energy of the car.
b) Find the amount of work done by the car as its front is pushed in.
c) Find the magnitude of the force that pushed the front of the car in by 54 cm.

## Homework Equations

Kinetic energy=1/2mass*speed^2

## The Attempt at a Solution

1/2*2436(10.7^2)=139449J of kinetic energy now what
Punt. Or since the problem asks for the change in KE, how much KE does it have when it stops, and what is its change? Then think the Work-Energy theorem.

got a and b now what about c

question C seems like its a little bit vague. This is my take on it. The car is going 10.7 m/s, and stops to 0 m/s in a distance of 54 centimetres. If you assume that it stops through a constant deceleration (which it probably wouldn't in a real situation), you can find out that deceleration. Once you've found that, you have the mass of the vehicle, and the deceleration of the vehicle, and you should be able to find the magnitude of the force.

question C seems like its a little bit vague. This is my take on it. The car is going 10.7 m/s, and stops to 0 m/s in a distance of 54 centimetres. If you assume that it stops through a constant deceleration (which it probably wouldn't in a real situation), you can find out that deceleration. Once you've found that, you have the mass of the vehicle, and the deceleration of the vehicle, and you should be able to find the magnitude of the force.
Or you could apply the definition of work. The force calculated is an average force.

Divide the work done (part b) by distance (0.54 m).

W = Fd
F = W/d

thanks

haha yeah that's definitely the right way. for some reason i read that it was a work and energy problem, and then decided to not take that into account during my response