Question

If a car at rest accelerates uniformly to a speed of 144km/h in 20s, it covers a distance:

Answer 1

  speed = 144km/h
          = 144*5/18 = 40m/s
apply
v = u + at
v = 40m/s
u = 0m/s
a = ?
t = 20 s
40 = 0 + 20*a
a = 2m/s²
apply
s = ut  + at²/2
s = ?
u = 0m/s
a = 2m/s²
t = 20s
s = 0 + 2*20²/2
s = 400m
hence car covers 400 meter.

Answer 2

speed = 144km/h = 40m/s
Using Newton's 1st equation,
v = u + at
40 = 0 + 20*a
a = 2m/s²
Using Newton's 2nd equation,
s = ut  + at²/2
s = 0 + 2*20²/2
s = 400m
Thus, the car covers 400 m.