# Finding acceleration of a car when it is braking

## Homework Statement

A 1200kg car moving at 20 metres per second stops in a distance of 50m when the brakes are applied.
a) What is the acceleration of the car when it is braking?
b) Find the force applied by the car's braking system.

## Homework Equations

For a) I used the acceleration formula: a=(velocity - initial velocity)/t
Time formula from rearranging: t=s/v

## The Attempt at a Solution

a)
t=s/v
t=50/20=2.5s

velocity=50/2.5=20 metres per second

a=(20-0)/2.5 = 8ms(^-2)[/B]
I do not know how to find the acceleration when BRAKING, and the answer claims that it is 4ms(^-2.)

As for b, I believe that I am unable to attempt it seeing as I am unable to find the acceleration.

Please explain how to do it! I have read through the chapter of my textbook, and am unable to understand. thank you very much!

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SteamKing
Staff Emeritus
Homework Helper

## Homework Statement

A 1200kg car moving at 20 metres per second stops in a distance of 50m when the brakes are applied.
a) What is the acceleration of the car when it is braking?
b) Find the force applied by the car's braking system.

## Homework Equations

For a) I used the acceleration formula: a=(velocity - initial velocity)/t
Time formula from rearranging: t=s/v

## The Attempt at a Solution

a)
t=s/v
t=50/20=2n5s

velocity=50/2.5=20 metres per second

a=(20-0)/2.5 = 8ms(^-2)[/B]
I do not know how to find the acceleration when BRAKING, and the answer claims that it is 4ms(^-2.)

As for b, I believe that I am unable to attempt it seeing as I am unable to find the acceleration.

Please explain how to do it! I have read through the chapter of my textbook, and am unable to understand. thank you very much!
Braking to a stop is just the reverse of accelerating to speed from a standing start.

Your equation t = s/v works only for constant speed. I have no idea what "2n5s" means.

There is a SUVAT equation which relates acceleration, distance, and initial and final velocities which would be rather useful here.