Waves · Question 11

Two cars moving in opposite directions approach each other with speed of 22 m s-1 and 16.5 m s-1 respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is (velocity of sound is 340 m s-1)

1. 361 Hz
2. 411 Hz
3. 448 Hz
4. 350 Hz

An air column, closed at one end open at the other, resonates with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is

1. 150 cm
2. 200 cm
3. 66.7 cm
4. 100 cm

A uniform rope of length L and mass m1 hangs vertically from a rigid support. A block of mass m2 is attached to the free end of the rope. A transverse pulse of wavelength 1 is produced at the lower end of the rope. The wavelength of the pulse when it reaches the top of the rope is 2. The ratio 2/ 1 is

1. m2m1
2. m1 + m2m1
3. m1m2
4. m1 + m2m2

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m s-1. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air = 330 m s-1)

1. 838 Hz
2. 885 Hz
3. 765 Hz
4. 800 Hz

The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length of the open pipe will be

1. L
2. 2L
3. L2
4. 4L

Three sound waves of equal amplitudes have frequencies (n - 1), n, (n + 1). They superimpose to give beats. The number of beats produced per second will be

1. 1
2. 4
3. 3
4. 2

A string is stretched between fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. The lowest resonant frequency for this string is

1. 10.5 Hz
2. 105 Hz
3. 155 Hz
4. 205 Hz

The fundamental frequency of a closed organ pipe of length 20 cm is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both the ends is

1. 120 cm
2. 140 cm
3. 80 cm
4. 100 cm

A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 m s-1 at an angle of 60 with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air 330 m s-1), is [figure]

1. 106 Hz
2. 97 Hz
3. 100 Hz
4. 103 Hz

If n1, n2 and n3 are the fundamental frequencies of three segments into which a string is divided, then the original fundamental frequency n of the string is given by

1. 1n = 1n1 + 1n2 + 1n3
2. 1 n = 1 n1 + 1 n2 + 1 n3
3. n = n1 + n2 + n3
4. n = n1 + n2 + n3