Circular track — A cyclist travels one lap (circumference) at 14.4 km/h in 1 min 28 s. Find the field’s area.
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A7958 sq m
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B9856 sq m
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C8842 sq m
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DCannot be determined
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E9056 sq m
Answer
Correct Answer: 9856 sq m
Explanation
Introduction / Context:One full lap around a circular field equals its circumference. Given speed and time, we find the distance per lap (circumference), then radius, and finally the area using A = πr^2.
Given Data / Assumptions:
- Speed = 14.4 km/h = 4 m/s
- Time = 1 min 28 s = 88 s
- Circumference C = speed * time
- π ≈ 22/7 for exact result here
Concept / Approach:Compute C, then r = C / (2π), and area A = πr^2. Numbers are chosen for a clean r.
Step-by-Step Solution:C = 4 * 88 = 352 mr = 352 / (2 * 22/7) = 352 / (44/7) = 352 * 7 / 44 = 56 mA = πr^2 = (22/7) * 56^2 = (22/7) * 3136 = 22 * 448 = 9856 sq m
Verification / Alternative check:With r = 56 m, circumference is 2πr = 2 * (22/7) * 56 = 352 m, which matches the distance covered.
Why Other Options Are Wrong:7958 and 8842 sq m come from rounding or π ≈ 3.14 without keeping the exact nice fraction; “Cannot be determined” is false because data are sufficient.
Common Pitfalls:Not converting km/h to m/s; mixing up diameter and radius in circumference calculations.
Final Answer:9856 sq m