ACT Science Practice Question #1787 (Hard (530)) | Test Citadel
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ACT Science Difficulty: Hard (530)

Digital ACT Science Practice Question #1787

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If an ambulance siren approaches a stationary pedestrian and then passes, the pedestrian will hear: Experiment Context (Acoustic Doppler Shift Measurements): A sound source emitting a steady 1,000 Hz tone moved along a straight track past a stationary microphone at various velocities (v) in air (speed of sound c = 340 m/s): Table 11: - Approaching at 17 m/s: Detected frequency = 1,053 Hz - Approaching at 34 m/s: Detected frequency = 1,111 Hz - Stationary (0 m/s): Detected frequency = 1,000 Hz - Receding at 17 m/s: Detected frequency = 952 Hz - Receding at 34 m/s: Detected frequency = 909 Hz
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Pitch drops when source changes from approaching to receding.

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Frequency drops from elevated approach pitch (>1,000 Hz) to lowered receding pitch (<1,000 Hz)....

Distractor Analysis: Trap choice eliminates careless test-takers who confuse roots with coordinates...

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