How do you work out the braking distance of a car?

Answer 1

First of all you need some data about your car telling how quickly it can slow down. So you can either find out the deceleration data of your car, or just measure how much time it takes to stop from a certain speed, which would be easier.

Lest say, travel at 30MPH, which is 13.4 meters per second. slam the brakes on and time how long it takes to stop.

With this data, we can work out the mean deceleration of your car in ms-2 by dividing 13.4 by however long it takes you to stop. lets say it takes 2 seconds, 13.4 / 2 = 6.7 so our deceleration is 6.7ms-2

We can then use a 'SUVAT' equation, namely s=ut+1/2at2 where:

u= Initial velocity (13.4 ms or your speed)

t= time (2 seconds or whatever your one is)

a= acceleration (-6.7)

s= displacement (distance)

so sub in (remember our acceleration is minus because we are slowing down): S=13.4*2+0.5*-6.7*(2*2)

This gives us 26.8+(-13.4) = 26.8-13.4 = 13.4 Meters

The Highway agency braking distance value for 30MPH is 14 meters, so that's pretty close.

So to do it yourself, convert your speed to meters per second, measure how long it takes to stop and sub your data into the above equations.

Happy calculating!