Question

A car is initially travelling at 30m/s, which is above the speed limit. The driver sees a speed limit trap ahead and applies the brakes for 5 seconds, causing the car to slow down by 2m/s every second while the brakes are on.
How far does the car travel while the brakes are being applied?

Answer 1

dv/dt = a = -2 m/s^2

v = 30 - a t

d = Vi t + .5 a t^2
so
d = 30 t - 1 t^2
but t = 5
so
d = 30*5 - 25
= 150 - 25 = 125