Motorcycle speed from wheel revolutions:\nA motorcycle wheel of diameter 70 cm makes 40 revolutions in 10 seconds. Find the speed of the motorcycle in km/h.

Introduction / Context:
Distance traveled equals revolutions times circumference. Convert the resulting m/s to km/h.

Given Data / Assumptions:

• Diameter d = 0.70 m ⇒ circumference C = πd ≈ 2.199 m.
• 40 rev in 10 s ⇒ 4 rev/s.

Concept / Approach:
Speed v = rev rate * circumference.

Step-by-Step Solution:

Verification / Alternative check:
Using π ≈ 22/7 gives the same rounded value.

Why Other Options Are Wrong:
They reflect incorrect circumference or conversion factors.

Common Pitfalls:
Forgetting to convert m/s to km/h by 3.6.

Final Answer:
31.68 km/h.