Question

This question is typical on some driver's license exams: A car moving at 50 km/h skids 15 m with locked brakes. How far will the car skid with locked brakes at 150 km/h?

Answer 1

Answer: 135 m

Explanation: In order to solve this problem we have to use the kinematic equations given by:

Xf= vo-(a/2)*t^2

Vf=vo-a*t

then we have for the first case:

t=vo/a

15 m= (vo^2/)a- (a/2)*vo^2/a^2= vo^2/2a

then a = (50 km/h*(1000/3600))^2/2*15= 6.43 m/s^2

With this value of the acceleration we solve the set of equation for an initial speed of 150 km/h

xf= vo^2/2a= 150*(1000/3600)^2/(2*6.43)=135 m