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(1) Two trains of equal length and moving with the same speed of 54 km/h in opposite directions cross each other in 10 sec. Find the length of the trains.

(2) The speed of a boat in still water is 8 km/h. If the boat covers a distance of 16.5 km upstream in 3 hours, find the speed of the current. PLZZ HELP..... THANKS!!

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====================== Length = L meters. The trains are moving with constant speed = v = 54 km/h = 54 * 5/18 = 15 m/sec

We use the concept of relative velocity. Let us view from the reference of one train. With respect to a person on one train, the other train is travelling with twice the speed = 15 + 15 = 30 m/sec.

The distance to be travelled is 2 * train length = 2 * L meters.

Hence, the time taken = distance / speed = 2 L / 30 = 10 sec => L = 150 meters. ================================ 2) Speed of boat = V = 8 km/hr velocity of current in river = R km/hr

when a boat travels upstream its velocity = V - R = (8 - R) km/h

distance covered = speed * time duration => 16.5 km = (8 - R) * 3 hours => 8 - R = 16.5/3 = 5.5 km/hr R = 2.5 km/h