Question

A car is speeding along the motorway at 40 m s when the driver
observes an accident ahead. He slams on the brakes, the wheels lock immediately, and the car skids to a halt. You may assume that the car travels in a straight line whilst it is skidding and that the magnitude of its deceleration is 10 m s^-2.
What distance does the car travel between the time that the brakes are applied and the time that the car comes to rest, and how much time does this take?

Answer 1

time to stop = t
v = Vi - 10 t
0 = 40 - 10 t
t = 4 seconds to stop
d = average speed during stop * time = 20 * 4 = 80 meters

Answer 2

a. V^2 = Vo^2 + 2a*d = 0,
40^2 + (-20)d = 0,
d = 80 m.

b. V = Vo + a*t = 0,
40 + (-10t = 0,
t = 4 s.