Question

When a driver presses the brake pedal, his car stops with an acceleration of -0.5 m/s2. How far will the car travel while coming to a complete stop if its initial speed was 8 m/s?

A. 16 m
B. 32 m
C. 64 m
D. 8 m

Answer 1

see we have been given
initial speed = u = 8 m/s
and acceleration a = -0.5 m/s^2
and we need to find how much distance will the car travel before comin to rest i.e. final speed v =0
so we know that
v^2-u^2 = 2as
we need to find s
0^2 - 8^2 = 2 * -0.5 * S
solvint it we get
S = -64/-1
S = 64 m
so Option C

Answer 2

Alternatively, find how long the cars slows down, t = v/a = 8/.5 = 16 sec.

Next use

s = v t - (1/2) a t^2 = 8*16 - (0.25) (16)^2 = 64,

agreeing, as they should.