You are here
Question
A runner completes 400 metres in 50 seconds. Another runner completes the same distance in 45 seconds. Who has a greater speed and by how much?
🔗 Concept: 8.3 Speed
Two runners, 400 m — who is faster and by how much?
![Question 2 - A runner completes - Measurement of Time an - [Teachoo] - Questions at the end of the chapter](https://cdn.teachoo.com/test/0da032b8-2a73-4845-b5a7-a072118369fd/image-two-runners-crossing-a-400-m-finish-line-one-arrives-at-50-s-and-another-at-45-s-showing-different-speeds.png)
Show Answer
Runner B (45 s) is faster by ≈ 0.89 m/s
Explanation
📋 Given
- Runner A: distance = 400 m, time = 50 s
- Runner B: distance = 400 m, time = 45 s
🔄 Unit Conversion
- No conversion needed — distance in m, time in s → speed in m/s.
📐 Formula
Speed = Distance ÷ Time
Step 1 — Speed of Runner A
$$\text{Speed}_A = \frac{400 \text{ m}}{50 \text{ s}} = 8 \text{ m/s}$$
Step 2 — Speed of Runner B
$$\text{Speed}_B = \frac{400 \text{ m}}{45 \text{ s}} \approx 8.89 \text{ m/s}$$
Step 3 — Compare
Runner B has a higher speed (less time for same distance).
$$\text{Difference} = 8.89 - 8 = \boxed{0.89 \text{ m/s}}$$
Runner B is faster — 8.89 m/s vs 8 m/s, difference ≈ 0.89 m/s.
