Reach for the Summit - P-S1-A1

A UFO is moving at a constant velocity vv from OO along ray OBOB, and OAOA is horizontal, as shown in the picture. Alice is observing it at point AA, and BOA=θ\angle BOA = \theta, which can be considered constant during the observation.

Given that the UFO is giving off a small pulse of sound wave and then a big pulse after τ (τ0)\tau\ (\tau \rightarrow 0) seconds.

If OA=LOA=L, and the speed of sound in the air is vv', at what condition for vv can Alice record the big pulse first and then the small pulse of sound wave?

Take θ=30°\theta = 30 \degree, and the condition is v>λvv > \lambda v'. Submit 1000λ\lfloor 1000\lambda \rfloor.

Reach for the Summit problem set - Physics


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