23. A train running at 54 km/ph takes 20 seconds to pass a platform.Next it takes 12 seconds to pass a man walking at 6km/ph in the same direction in which the train is going.Find the length of the train and the length of the platform?

A. 135 m B. 142 m C. 140 m D. 138 m

Answer Answer: Option C Explanation: Let the length of the train be X meters and length of platform be Y meters.
Speed of the train relative to man = (54-6) km/ph =48 km/ph = (48*5/18)m/sec = 40/3 m/sec
In passing a man the train covers its own length with relative speed.
Length of train =(relative speed * time) = (40/3*12)m =160m
Also speed of the train =(54*5/18)m/sec = 15 m/sec
Hence x+y/15 =20
x+y = 300
y= (300 -160) m = 140 m

24. A train passes a station platform in 36 seconds and a man standing on the platform in 20 seconds.If the speed of the train is 54 km/hr,what is the length of the platform?

A. 120 m B. 240 m C. 300 m D. None of these

Answer Answer: Option B Explanation: Speed = (54*5/18) m/sec = 15 m/sec.
Length of the train =(15*20) m = 300m
Let the length of the platform be X meters
Then X+300/36 = 15<=> X+300 = 540 <=> X= 240m