A source of sound moves away with the velocity of sound from a stationary observer. The frequency of the sound heard by the observer:

1. remains the same

2. is doubled

3. is halved

4. becomes infinity
 

The longitudinal waves can travel :

1.  only in liquids

2.  only in solids

3.  only in gases

4.  In liquids, solids, and gases

The equation of a wave pulse travelling along x-axis is given by $y=\frac{30}{2+{\left(x-20t\right)}^2}$, x and y are in meters and t is in seconds. The amplitude of the wave pulse is 

1.  5 m

2.  20 m

3.  15 m

4.  30 m

The equation of a standing wave in a string is $\mathrm{y}=\left(\mathrm{200 }\mathrm{m}\right)\sin \frac{2\mathrm{\pi }}{50}\mathrm{x\; cos}\frac{2\mathrm{\pi }}{0.01}\mathrm{t}$ where x is in meters and t is in seconds. At the position of antinode, how many times does the distance of a string particle become 200 m from its mean position in one second?

Eleven tuning forks are arranged in increasing order of frequency in such a way that any two consecutive tuning forks produce 4 beats per second. The highest frequency is twice that of the lowest. The highest and the lowest frequencies (in Hz) are, respectively:

Consecutive frequencies emitted from an organ pipe are 75Hz, 125Hz, 175Hz.  The frequency of the tenth overtone will be:

The sound intensity level at a point 10 m away from a point source is 20dB, then the sound level at a distance 1m from the same source would be

(1) 40 dB

(2) 30 dB

(3) 200 dB

(4) 100 dB

In the phenomenon of interference of sound by two coherent sources if difference of intensity at maxima to intensity at minima is 20dB, then the ratio of intensities of the two sources is

1.  $\frac{121}{81}$

2.  $\frac{11}{9}$

3.  $\frac{101}{99}$

4.  $\frac{10}{1}$

When a sound wave travels from one medium to another, the quantity that remains unchanged is :

1.  speed

2.  amplitude

3.  frequency

4.  wavelength

If a sound source of frequency n approaches an observer with velocity v/4 and the observer approaches the source with velocity v/5, then the apparent frequency heard will be-

1.  (5/8)n

2.  (8/5)n

3.  (7/5)n

4.  (5/7)n