# Driving a car

1. Jan 21, 2013

### helpme2012

1. The problem statement, all variables and given/known data

You are driving your car and you heavily apply the brakes for a period of 2.1 seconds. The car keeps moving for a distance of 14.6m before it completely stops.

What is the acceleration (in m/s2) experienced by the car? Is it truly "acceleration"?

2. Relevant equations

5 kinematic equations

3. The attempt at a solution
I was using this : Δd=VfΔt-0.5aΔt2

14.6=0(2.1)-0.5a(2.12)
14.6= 0-0.5a(4.41)

I don't know what to do after that, I don't know what to do with the part of the equation with the acceleration. Am I even using the right kinematic equation?

2. Jan 21, 2013

### CompuChip

You are using the right one! Note how you have a single equation with just one unknown, a - which is exactly what you're after.
So much for the physics part, you need to pull out your mathematical skills now and solve the equation. First, try simplifying 0.5 * 4.41 and 0 - ....

3. Jan 21, 2013

### HallsofIvy

Staff Emeritus
Notice the "0- " part. The acceleration will be negative. In everyday language we would call that "deceleration" but, technically, it is still a type of "acceleration".

4. Jan 21, 2013

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