Question

There are two laps in a race. An athlete ran the first lap at an average speed to 20 m/s. However, he could manage an average speed of only 10 m/s in the second lap. What is his average speed for the complete race?

• A. 11.67 m/s
• B. 12.50 m/s
• C. 13.33 m/s
• D. 15 m/s

Answer 1

The Correct Option is C

Step 1:

Let the distance of each lap be d. 

The time taken for the first lap is:

Time for first lap = \( \frac{d}{20} \).

The time taken for the second lap is:

Time for second lap = \( \frac{d}{10} \).

Step 2:

The total time for the race is:

Total time = \( \frac{d}{20} + \frac{d}{10} \) = \( \frac{d}{20} + \frac{2d}{20} \) = \( \frac{3d}{20} \).

Step 3:

The total distance for the race is 2d.

The average speed is:

Average speed = \( \frac{\text{Total distance}}{\text{Total time}} \) = \( \frac{2d}{\frac{3d}{20}} \) = \( \frac{2d \times 20}{3d} \) = \( \frac{40d}{3d} \) = \( 13.37 \) m/s.

Conclusion:

The average speed is 13.37 m/s.