Question

Two trains 121 m and 99 m in length are running in opposite  directions with velocities 40 km/h and 32 km/h. In what time they  will completely cross each other?
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Answer 1

Explanation:

consider relative motion then the total distance to be covered is 220m with a velocity of 72kmph means 20m/s , the time taken is 220/20 = 11 seconds