DP Physics (last assessment 2024)

Question 22N.1.HL.TZ0.29

Date	November 2022	Marks available	[Maximum mark: 1]	Reference code	22N.1.HL.TZ0.29
Level	HL	Paper	1	Time zone	TZ0
Command term		Question number	29	Adapted from	N/A

29.

[Maximum mark: 1]

22N.1.HL.TZ0.29

An ambulance emitting a sound of frequency $f$ is moving towards a point X at a velocity of +40 m s⁻¹. A car is moving away from X at a velocity of +20 m s⁻¹.

The speed of sound is $v$ .

What is the frequency detected in the car?

A. $f \frac{(v - 20)}{(v - 40)}$

B. $f \frac{v}{(v - 20)}$

C. $f \frac{(v + 20)}{(v + 40)}$

D. $f \frac{(v + 20)}{(v - 40)}$

[1]

Markscheme

Examiners report

A difficult question with only about one third of the candidates answering it correctly. A popular incorrect choice was B, indicating a misconception that the Doppler effect in air only depends on the relative velocity of the source and the observer, rather than on each of these velocities relative to the medium. The question requires an assumption that the air is still relative to the ground and point X.

Syllabus sections

Additional higher level (AHL)

Additional higher level (AHL) » Topic 9: Wave phenomena » 9.5 – Doppler effect

Additional higher level (AHL) » Topic 9: Wave phenomena

Question 22N.1.HL.TZ0.29

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