Question 04
A train moves past a telegraph post and a bridge 264 m long in 8 seconds and 20 seconds respectively. What is the speed of the train?
Let length of the train be z meter
Given, time taken by the train to cross the telegraph post = 8 seconds
Since, Speed of the train = Length of the train/Time taken to cross the telegraph
= z/8 ………………………………………………eq.(1)
And, time taken by the train to cross the 264 m long bridge = 20 seconds
Since, Speed of the train = (Length of the train + Length of the platform)/ Time taken to cross the platform
= (z + 264)/20 …………………………………eq.(2)
From eq.(1) and eq.(2)
z = z + 264
20z = 8 (z + 264)
20z = 8z + 2112
20z – 8z = 2112
12z = 2112
z = 2112/12
z = 176 m
putting value of z = 176 in eq.(1)
Speed of the train = 176/8
= 22 m/sec.
= 22 * (18/5) km/hr.
= 79.2 km/hr.