A boat moves with a speed of 5 km/h relative to water in a river flowi...
Problem:
A boat moves with a speed of 5 km/h relative to water in a river flowing with a speed of 3km/h and having width of 1km. The time taken around a round trip is A)5min B)30min C)10min? Explain in details.
Solution:
Let's assume that the boat is moving in the direction perpendicular to the river flow. In this case, the speed of the boat relative to the ground is given by:
Speed of boat relative to ground = Speed of boat relative to water + Speed of water
Substituting the given values, we get:
Speed of boat relative to ground = 5 km/h + 3 km/h = 8 km/h
Time taken to cross the river:
Let's assume that the width of the river is 1 km. In this case, the time taken by the boat to cross the river is given by:
Time taken to cross the river = Distance / Speed = 1 km / 5 km/h = 0.2 hours = 12 minutes
Time taken to return:
When the boat returns, it will be moving in the direction opposite to the river flow. In this case, the speed of the boat relative to the ground is given by:
Speed of boat relative to ground = Speed of boat relative to water - Speed of water
Substituting the given values, we get:
Speed of boat relative to ground = 5 km/h - 3 km/h = 2 km/h
Using the same formula as before, the time taken by the boat to cross the river on its return journey is given by:
Time taken to cross the river = Distance / Speed = 1 km / 2 km/h = 0.5 hours = 30 minutes
Total time:
The total time taken by the boat to complete the round trip is given by:
Total time = Time taken to cross the river + Time taken to return = 12 minutes + 30 minutes = 42 minutes
Therefore, the correct answer is B) 30 minutes.