Question

a train in crossed a 140 m long platform in 15 sec and a 180 m long platform in 17 sec .the speed of train was

Answer 1

The train covers 162 - 120 = 42 m in 18 - 15 = 3 seconds.

=> Speed of train = 42/3 = 14 m/s

The train covers 18 x 14 = 252 m in 18 seconds.

=> Length of train = 252 - 162 = 90 m.

Traditional Method :

Let length of train = L

In first case, train covers 162 + L m in 18 seconds and in second case train covers 120 + L m in 15 seconds.

Speeds are (162 + L)/18 and (120 + L)/15 respectively.

But they are equal.

=> (162 + L)15 = (120 + L)18

=> 2430 - 2160 = 3L

=> L = 270/3 = 90 m

Answer 2

140 m in 15 sec
and 180 m in 17 sec
so 320 m in 32 sec
= 10 m/s
=600 m in minute
=36000 m/h
= 36 km/h