- #1

- 5

- 0

## Homework Statement

A car is driving at a speed of 72km/h. It starts to slow down and it stops after 10s. How long is the trail of braking ?

## Homework Equations

t - time

a - acceleration

v0- starting speed

v - final speed

## The Attempt at a Solution

So in my book it says that if a object is slowing down the acceleration is negative and the formula for acceleration is a=v-v0\t, assuming that v0=72km/h=20m/s and v=0 , the acceleration is..:

a = -2m/s^2

So if the acceleration is negative then the distance s= v0t - at^2/2..

After some calculating I get that s=300m... But in my book there are solutions and it says that a = 2m/s^2 and that s = 100m... I don´t get it. Please help I need it today.. Thanks :D

Btw. sorry for my bad English :P