Question

When the brakes are applied, the speed of a car decreases from 12 m/s to 9 m/s in 3 s. How long does it take for the car to come to rest?

Answer 1

Let the initial speed and final speed of body be 'u' and 'v' respectively, time be 't' and distance.
u = 12 m/s
v = 9 m/s
t = 3 s
a = ?
S = ?
a = (v-u)/t
  = (9-12)/3
  = -1 m/s²
v² = u² + 2aS
9² = 12² + 2X(-1)XS
81 = 144 -2S
-2S = 81-144
S = -63/-2
S = 31.5 m