1.

A train of length 180 metres crosses a tree in 15 seconds and crosses another train of the same length travelling in opposite direction in 20 seconds. What is the speed (in km/hr) of the second train?1). 21.62). 63). 33.44). 36.6

Answer»

Time taken to cross the tree = Length of train/SPEED of train

⇒ Speed of train = 180/15 = 12 m/sec.

Let the speed of the second train be ‘x’ m/sec.

? The TRAINS are moving in opposite directions, HENCE, their relative speed is the sum of their individual speeds

⇒ Relative speed = x + 12

Now,

Time taken to cross each other = Sum of lengths of trains/Relative speed

20 = (180 + 180)/(x + 12)

⇒ x + 12 = 360/20

⇒ x = 18 - 12 = 6 m/sec.

∴ Speed of second train = 6 × 18/5 = 21.6 km/hr.


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