Question

The speed of the stream is 25 kmph. The speed of the boat downstream is 15 m / s. Find the speed of the boat in still water.

• A. 8.06 m/s
• B. 6.05 m/s
• C. 5.23 m/s
• D. 8.56 m/s

Hint:

Downstream speed is always the highest speed because the water helps the boat. Still water speed is simply the average of Upstream and Downstream speeds.

Answer 1

The Correct Option is A

Concept: Downstream Speed (\(D\)) = Speed of boat in still water (\(u\)) + Speed of stream (\(v\)). \[ u = D - v \]
Step 1: Convert the stream speed to m/s.
Speed of stream (\(v\)) = 25 kmph.
\(v \text{ (in m/s)} = 25 \times \frac{5}{18} = \frac{125}{18} \approx 6.944 \text{ m/s}\).

Step 2: Find the speed of the boat in still water.
Downstream speed (\(D\)) = 15 m/s. \[ u = 15 - 6.944 = 8.056 \approx 8.06 \text{ m/s}. \]