# Stopping distance of a car?

1. Sep 15, 2015

### David Donald

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

While traveling on the highway with your 1000kg car, at 115.2 km/h, where you’re ABS (automatic

braking system) is disabled. This means braking is relying solely on the friction of your tires with the road when they stop spinning. A dear jumps into the road 50 meters in front of you. If the frictional force created by you slamming on your brakes is 4000N. What will your final stopping distance be? Will you

hit the dear? Assume no air resistance.

2. Relevant equations

Kinematics?

3. The attempt at a solution
Sum of Forces in The X direction
(Force O' Car) - (Force O' Friction) = -ma

I solved for acceleration and got -5.8 m/s^2
plugging these into the kinematics equation I got a time... 5.52 seconds
plugging that into the Xf = Xo + Vox t + 1/2 a t^2 I got a distance which is wrong

what gives? what am i doing wrong?

2. Sep 15, 2015

### RUber

3. Sep 15, 2015

### RUber

4. Sep 15, 2015

### SteamKing

Staff Emeritus
When someone tells you, "Be a dear," they don't mean for you to drop down on all fours while wearing a hat rack on your head.

"Deer" is the animal which jumps out in front of the car.

5. Sep 15, 2015

### David Donald

Ok... So I am not able to get to the same acceleartion I was getting before so now I'm really confused

Since the only thing acting on the car when its stopping is the breaking force would it be

Sum Fx = -Fbrakes = ma ?

6. Sep 15, 2015

### RUber

That's right.