A boat moves at 21 km/hr downstream and at 13 km/hr upstream in a river. A coconut falls into the same river and floats freely with the current. How long will the current take to carry the coconut 14 km?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 3 hours 30 minutes
A freely floating coconut has no speed of its own; it moves only with the current. The current’s speed is half the difference of the downstream and upstream speeds of the boat.
Speed of the current \(\displaystyle =\frac{21-13}{2}=4\) km/hr
Time for 14 km \(\displaystyle =\frac{14}{4}=3.5\) hours
\(0.5\) hour \(=30\) minutes, so the time is 3 hours 30 minutes