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A runner completes one lap of a circular track of radius \(R\) in 40 seconds. What is the runner's displacement after 2 minutes and 20 seconds?

1. Zero
2. 2R
3. 2*pi*R
4. 7*pi*R

Correct answer: 2R

Solution

Time taken = 140 s, and one lap takes 40 s, so the runner completes 3.5 laps. After 3 full laps the runner is back at the start, and after the extra half lap the runner is diametrically opposite the starting point, so displacement magnitude is the diameter \(2R\).

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