Question

A car moves in a straight line with constant acceleration. Starting from rest at t=0 it travels 8.0 m in 4.0 s. What is the speed of the car at t= 4 s.

PLEASE explain :)

Answer 1

d = (1/2) a t^2
8 = .5 a (16)

so a = 1 m/s^2

v = a t = 1 (4) = 4 m/s

or use head like this
average speed = 8 m/4s = 2 m/s
begin speed is zero
so final speed = twice average speed = 2*2 = 4 m/s