Question

A train with a constant velocity of +28.6 m/s approaches a small town . the operator applies the brake, reducing the train's velocity to +11.4 m/s. if the average acceleration of the train during braking is 1.35 m/s2, for what elapsed time does the operator apply the brake?

Answer 1

We shall use the formula
v = u + at
where
v = final velocity
u = intal velocity
t = time
a =  acceleration

For the given problem,
v = 11.4 m/s (final elocity)
u = 28.6 m/s (initial velocity)
a = -1.35 m/s^2  (negative acceleration for braking)

Therefore
11.4 = 28.6 - 1.35t
1.35t = 28.6 - 11.4 = 17.2
t = 17.2/1.35 = 12.7407 s

Answer:  12.74 s