Waves Test

Result

Waves Test - 91

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Weekly Quiz Competition

Question 1
4 / -1

A table is revolving on its axis at 5 revolutions per second. A sound source of frequency 1000 Hz is fixed on the table at 70 cm from the axis. The minimum frequency heard by a. listener standing at a distance from the table will be (speed of sound = 352 m/s)

A
1000 Hz

B
1066 Hz

C
941 Hz

D
352 Hz

Solution
Question 2
4 / -1

A train approaches a stationary observer, the velocity of train being 1/20 of the velocity of sound. A sharp blast is blown with the whistle of the engine at equal intervals of a second. The interval between the successive blasts as heard by the observer is

A

B

C

D

Solution
Question 3
4 / -1

A source of sound of frequency n is moving towards a stationary observer with a speed S. If the speed of sound in air is V and the frequency heard by the observer is n19 the value of n₁/n is

A
(V + S)/V

B
V/ (V + S)

C
(V - S)/V

D
V / (V - S)

Solution
Question 4
4 / -1

A vehicle with a horn of frequency n is moving with a velocity of 30 m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency n + n₁. Then (if the sound velocity in air is 300 mis)

A
n₁ = 1.0 n

B
n₁ = 0

C
n₁ = 0.1n

D
n₁ = – 0.1n
Question 5
4 / -1

A whistle giving out 450 Hz approaches a stationary observer at a speed of 33 m/s. The frequency heard by the observer in Hz is

A
409

B
429

C
517

D
500

Solution
Question 6
4 / -1

An observer standing at station observes frequency 219 Hz where a train approaches and 184 Hz when train goes away from him. If velocity of sound in air is 340 m/s, then velocity of train and actual frequency of whistle will be

A
15.5 ms^–1, 200 Hz

B
19.5 ms^–1, 205 Hz

C
29.5 ms^–1, 200 Hz

D
32.5 ms^–1, 205 Hz

Solution
Question 7
4 / -1

At what speed should a source of sound move so that stationary observer finds the apparent frequency equal to half of the original frequency?

A
v/2

B
2v

C
v/4

D
v

Solution
Question 8
4 / -1

A boy is walking away from a wall towards an observer at a speed of 1 metre/sec and blows a whistle whose frequency is 680 Hz. The number of beats heard by the observer per second is (Velocity of sound in air = 340 metres/sec)

A
Zero

B
2

C
8

D
4

Solution
Question 9
4 / -1

The driver of a car travelling with speed 30 metres per second towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 metres per second, the frequency of the reflected sound as heard by the driver is

A
720 Hz

B
555.5 Hz

C
550 Hz

D
500 Hz

Solution
Question 10
4 / -1

Two sirens situated one kilometer apart are producing sound of frequency 330 Hz. An observer starts moving from one siren to the other with a speed of 2 m/s. If the speed of sound be 330 m/s, what will be the beat frequency heard by the observe

A
8

B
4

C
6

D
1

Solution