We know that, if two trains are running in the same direction, then relative speed is equal to the difference of the speeds of both the trains.
? Required relative speed = 21 - 15 = 6 km/h
When two trains are moving in opposite directions then their relative speed is equal to the sum of the speed of both the trains.
? Required relative speed = 6 + 12 = 18 m/s
Length of platform is not given. it can not be determined.
By the formula, speed= Distance/ Time
= (240 + 240)/27 x (18/5)
= 480/27 x 18/5 = 64 km/h
We know that,
Speed = Distance/ Time
Speed of the train = 220/12 x (18/5) km/h
We know that, the distance covered by a train in passing a pole or a standing man or a signal post or any other object (of negligible length) is equal to the length of the train.
In this case, train covers 90 m to cross a standing man.
? Length of the train = 90 m
Relative speed of train
= Speed of train + Speed of car
? 90 = Speed of train + 15
? Speed of train = 90 - 15 = 75 km/h
Speed of the train = 18 km/h = 18 x 5/18 m/s = 5 m/s
Distance covered = Length of the train = 120 m
? Time taken by the train to cross the man = Distance/Speed
= 120/5 = 24 s
Speed of train = (120/5) = 24 m/sec.
Time takes to cross the platform
= (120 + 180)/24
= 121/2
Length of train = 120 m.
Total taken in crossing the pole = 10 seconds.
Speed of the train = length / time
= 120 / 10
= 12 m/s
= 12 x (18/5)
= 43.2 km/hr
Let the required distance be x km.
Then, ( x/80 ) - ( 220 - x ) / 100 = 1/2
? 5x - 4( 220 - x ) = 200
? 9x = 1080
? x = 120 km
? Required distance = 120 km
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