Important Concepts & Tricks – Boat and Stream

Up Stream – It means the boat is moving against the direction of the stream.

Down Stream – It means the boat is moving in the direction of the stream.

Note-

  1. Stream means current i.e. the speed of the water.
  2. When we say the speed of boat/swimmer/steamer, we mean the speed in still water.
  3. Speed of Boat/Steamer/swimmer is always considered greater than the speed of the current.

Let the Speed of Boat = x km/hr

Speed of Stream/current = y km/hr. Then-

Speed of Boat in Upstream = (x – y) km/hr

Speed of Boat in downstream = (x + y) km/hr

Speed of Boat = 1/2 (Speed of Boat in Upstream + Speed of Boat in downstream)

Speed of Stream = 1/2 (Speed of Boat in downstream – Speed of a boat in Upstream)


Boat and Stream Examples-

Q- 1. A man can row upstream at 6 km/hr and downstream at 10 km/hr. Find the speed of man and the speed of the current.

Upstream Speed= 6 km/hr

Downstream Speed = 10 km/hr

Man’s Speed = (10 + 6)/2 = 8 km/hr (Answer)

Current’s Speed = (10 – 6)/2 = 2 km/hr (Answer)

Q- 2. A boat can travel with a speed of 11 km/hr in still water. If the speed of the stream is 6 km/hr, find the time taken by the boat to go 85 km downstream.

Solution-

Downstream Speed- (11+6) = 17 km/hr

Time taken to travel 85 km- (dist./speed) = 85/17 = 5 hours (Answer)


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