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Wave Systems · Part 3 of 3
6 exam-style questions with model answers, plus 8 quick multi-choice questions — every question on this part of the standard, grouped by the 2 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
An ambulance with its siren on drives toward a stationary observer.
State whether the observer hears a frequency higher or lower than the emitted frequency, and state what happens to the wavelength reaching the observer.
A train sounds its horn at a constant frequency as it travels away from a stationary observer at constant speed.
Explain why the observer hears a lower frequency than the horn emits, and state what happens to the speed of the sound waves.
A student listening to a racing car pass at high speed claims: "The pitch slides smoothly down as the car goes by, because the sound waves are slowed down by the time they reach me once the car has passed."
Discuss this claim fully. Correct both parts of it, explain what the observer actually hears and why, and explain what would change if the car travelled faster.
A siren emitting Hz moves toward a stationary observer at m s−1. The speed of sound is m s−1.
Calculate the frequency heard by the observer.
A train whistle emits Hz. The train passes a stationary observer at m s−1 (speed of sound m s−1).
Calculate the frequency the observer hears as the train approaches and as it recedes, and explain why the two shifts are not equal in size.
A stationary observer beside a straight road measures the sound of a passing motorcycle. As it approaches they measure Hz, and after it has passed they measure Hz. The speed of sound is m s−1.
Determine the frequency emitted by the motorcycle and its speed. Then explain why the emitted frequency is not simply the average of the two measured frequencies.