Question

A train slow down from 108 kilometer per hour with a uniform retardation of 5 meter per seconds how long will it take to reach 18 kilometer per hour

Answer 1

a = -5 m/s^2 ??

108 km /hr * (1 hr / 3600 s) * (1000 m / 1 km) = 30 m/s
18 km/hr /3.6 = 5 ms
so
v = Vi + a t
5 = 30 - 5 t
5 t = 25
t = 5 seconds