Question

A train of length 100 m crosses another train of length 150 m, running on a parallel track in the opposite direction in 9 seconds. If the speed of train
having length 150 m is 40 km/hr, then what is the speed (in km/hr) of the other train?

Answer 1

Relative speed of trains=(100+150)/9 m/s
=250/9*18/5=100km/hr
And relative speed= speed 1st train +speed 2nd train =40+2nd train=100
Hence
Speed of second train =60km/hr

Answer 2

Total distance = 100 + 150 = 250 m

Time taken = 9 sec

Distance covered by the Train with length 150m:

1 hour = 40 km

1 sec = 40 ÷ 3600 = 1/90 km

9 sec = 1/90 x 9 = 1/10 km = 100m

Distance covered by the train with length 100m:

250 - 100 = 150m

Find Speed of the train with length 100m

9 sec = 150m

1 sec = 150/9 km

1 hour = 150/9 x 3600 = 60000m = 60 km

Speed = 60km/h

Answer: 60km/h