A boat can travel at 21 km/h in still water. If the speed of the stream is 3…
2026
A boat can travel at 21 km/h in still water. If the speed of the stream is 3 km/h, find the time taken by the boat to travel 48 km downstream.
Answer: D. 2 hours — ConceptFor downstream motion, the stream assists the boat, so downstream speed equals the speed in still water plus the speed of the stream. Time is…
- A.
3 hours
- B.
2 hours 20 minutes
- C.
3 hours 10 minutes
- D.
2 hours
Attempted by 78 students.
Show answer & explanation
Correct answer: D
Concept
For downstream motion, the stream assists the boat, so downstream speed equals the speed in still water plus the speed of the stream.
Time is calculated using time = distance ÷ speed, with compatible units.
Application
The speed of the boat in still water is 21 km/h and the speed of the stream is 3 km/h.
Downstream speed = 21 + 3 = 24 km/h.
Time for 48 km downstream = 48 ÷ 24 = 2 hours.
Cross-check
Using distance = speed × time gives 24 × 2 = 48 km, which matches the given distance.
Therefore, the required time is 2 hours.