Waves Test

Result

Waves Test - 69

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Weekly Quiz Competition

Question 1
4 / -1

A small source of sound moves on a circle as shown in the figure and an observer is standing on O . Let n₁, n₂ and n₃ be the frequencies heard when the source is at A, B and C respectively. Then

A
n₁ > n₂ > n₃

B
n₂ > n₃ > n₁

C
n₁ = n₂ > n₃

D
n₂ > n₁ > n₃

Solution
Question 2
4 / -1

A source emits a sound of frequency of 400 Hz, but the listener hears it to be 390 Hz. Then

A
The listener is moving towards the source

B
The source is moving towards the listener

C
The listener is moving away from the source

D
The listener has a defective ear
Question 3
4 / -1

A source and an observer are moving towards each other with a speed equal to v/2 where v is the speed of sound. The source is emitting sound of frequency n. The frequency heard by the observer will be

A
Zero

B
n

C

D
3n

Solution
Question 4
4 / -1

A police car horn emits a sound at a frequency 240 Hz when the car is at rest. If the speed of the sound is 330 m/s, the frequency heard by an observer who is approaching the car at a speed of 11 m/s, is :

A
248 Hz

B
244 Hz

C
240 Hz

D
230 Hz

Solution
Question 5
4 / -1

A person carrying a whistle emitting continuously a note of 272 Hz is running towards a reflecting surface with a speed of 18 km/hour. The speed of sound in air is 345 ms^–1. The number of beats heard by him is

A
4

B
6

C
8

D
3

Solution
Question 6
4 / -1

The speed of sound in air is 340 m/s. The speed with which a source of sound should move towards a stationary observer so that the apparent frequency becomes twice of the original

A
640 m/s

B
340 m/s

C
170 m/s

D
85 m/s

Solution
Question 7
4 / -1

A bat flies at a steady speed of 4 ms^–1 emitting a sound of f = 90 × 10³ Hz. It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as 330 ms^–1).

A
88.1 × 10³ Hz

B
87.1 × 10^–3 Hz

C
92.1 × 10³ Hz

D
89.1 × 10³ Hz

Solution
Question 8
4 / -1

A source of sound is approaching an observer with speed of 30 ms^–1 and the observer is approaching the source with a speed 60 ms^–1. Then the fractional change in the frequency of sound in air (330 ms^–1) is

A

B

C

D
Question 9
4 / -1

A police car with a siren of frequency 8 kHz is moving with uniform velocity 36 km/hr towards a tall building which reflects the sound waves. The speed of sound in air is 320 m/s. The frequency of the siren heard by the car driver is

A
8.50 kHz

B
8.25 kHz

C
7.75 kHz

D
7.50 kHz

Solution
Question 10
4 / -1

A source is moving towards a stationary observer, so that the apparent frequency increases by 50%. If velocity of sound is 330 ms^–1, then velocity of source is

A
220 ms^–1

B
180 ms^–1

C
150 ms^–1

D
110 ms^–1

Solution