Question

An electric train leaves a station starting from rest and attains a speed of 72km/hr in 10 second. Then it undergoes uniform retardation for 20 second to come to halt at the next station then calculate

i) the distance between the train stations.
ii) the average velocity of train.

Answer 1

d=1/2*10s*20m/s+1/2*20s*20m/s=100m+200m=300m avg velocity=total distance/total time=300/30=10m/s

Answer 2

a = 7.2km/hr-s
s = 1/2 * 7.2 * (10/3600)^2 + (72*20/3600 - 1/2 * 3.6 * (20/3600)^2) = .4km = 400m