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 ?
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