Question

The brakes of an automobile are suddenly applied at the instant when its velocity is 20 m/s. If the automobile comes to a stop after 5 seconds, what is its acceleration?

Answer 1

Data:

Time (t) = 5 seconds
Final Velocity (v) = 0 [as the car comes to rest]
Initial velocity (u) = 20 m/s
Acceleration = ? (Negative because it is braking)

$Acceleration = \frac{v-u}{t}$
$Acceleration = \frac{0-20}{5}$
$\boxed{Acceleration = - 4m/s^2}$