As we know, according to the equation of motion,
v = u + at
Given,
u = 90 km h-1 or 25 m s-1
v = 0 (as the train stops on application of brakes)
t = 10 s
retardation = -a = -0.5 m s-2
Substituting the values in the formula above we get,
v = 25 + (-0.5) × 10 = 20 ms-1
Hence, the velocity after 10 s = 20 m s-1.
(ii) As we know, according to the equation of motion,
v = u + at
Substituting the values in the formula above, to get the time taken by the train to come to rest.
0 = 25 + (-0.5 × t)
or, 0 = 25 – 0.5t
or, 0.5t = 25
or, t = 25/0.5 = 50 s
Hence, the time taken by the train to come to rest = 50 s.