Difficulty: Medium
Correct Answer: 28 m/s
Explanation:
Introduction / Context:
This is a moving-observer Doppler timing case. If the source emits with period T, an observer moving toward a stationary source perceives period T′ = T * (1 − v_o / v), where v_o is observer speed and v is sound speed. We compare the actual 6-minute interval with the heard 5 min 32 s.
Given Data / Assumptions:
Concept / Approach:
Use T′ = T * (1 − v_o / v). Solve for v_o = v * (1 − T′ / T). Round to the nearest option as practical measurement output.
Step-by-Step Solution:
Verification / Alternative check:
Using 28 m/s back into T′ ≈ 360 * (1 − 28/332) ≈ 360 * 0.9157 ≈ 330 s (near 332 s), within typical rounding tolerance for such problems.
Why Other Options Are Wrong:
56/102 m/s are unrealistically high for a car; 32 m/s overshoots the implied timing.
Common Pitfalls:
Using frequency formula directly without converting to period; mixing minutes and seconds.
Final Answer:
28 m/s
Discussion & Comments