Answer
Find out the calculate the acceleration if it took 3 seconds to slow your car down .
To prove
The formula of the accleration is given by
![a = \frac{v_{f} - v_{i}}{t}](https://tex.z-dn.net/?f=a%20%3D%20%5Cfrac%7Bv_%7Bf%7D%20-%20v_%7Bi%7D%7D%7Bt%7D)
![where\ v_{f}\ is\ the\ final\ velocity.](https://tex.z-dn.net/?f=where%5C%20v_%7Bf%7D%5C%20is%5C%20the%5C%20final%5C%20velocity.)
![where\ v_{i}\ is\ the\ intial\ velocity.](https://tex.z-dn.net/?f=where%5C%20v_%7Bi%7D%5C%20is%5C%20the%5C%20intial%5C%20velocity.)
t is the time.
As given
you are traveling in a car that is moving at a velocity of 20 m/s.
suddenly a car 10 meters in front of you slams on its brakes.
at the moment you also slam on your brakes and slow to 5 m/s and it take 3 seconds.
![v_{f} = 5m/s](https://tex.z-dn.net/?f=v_%7Bf%7D%20%3D%205m%2Fs)
![v_{i} = 20m/s](https://tex.z-dn.net/?f=v_%7Bi%7D%20%3D%2020m%2Fs)
t = 3s
put all the value in the formula
![a = \frac{5 - 20}{3}](https://tex.z-dn.net/?f=a%20%3D%20%5Cfrac%7B5%20-%2020%7D%7B3%7D)
![a = \frac{-15}{3}](https://tex.z-dn.net/?f=a%20%3D%20%5Cfrac%7B-15%7D%7B3%7D)
a = -5 m/s²
Therefore the acceleration is -5 m/s² .