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2 trains, 100 m and 120 m long are running in the same direction with speeds of 72 km/hr and 54 km/hr. In how much time will the first train cross the second?

Relative speed of trains = 72 - 54 = 18km/hr18km/hr = 5 m/sec

Distance = 100 + 120 = 220 mTime taken = Distance / SpeedTime taken = 220/5 = 44 sec

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A toy train crosses 210 and 122 m long tunnels in 25 and 17 sec respectively. Find the train's length.

Let length of train = x metersSpeed = Distance/TimeFirst distance = 210 + xTime = 25 sec

2nd distance = 122 + xTime = 17 sec

Speed = (210 + x)/25 = (122 + x)/17x = 65 m

A man sitting in a train which is travelling at 50 km/hr observes that a goods train, travelling in the opposite direction, takes 9 sec to pass him. If the goods train is 280 m long, find its speed.

Relative speed = Distance/TimeRelative speed = (280/9) m/sec = 112 km/hrSpeed of goods train = 112 - 50 = 62 km/hr

A train moves with a speed of 126 km/hr. Convert it to m/sec.

a km/hr = (a x 1000)/3600 m/sec

126 km/hr = (126*1000)/3600 m/sec

So 126 km/hr = 35 m/sec