NEET Physics Waves MCQs Set B

Question. Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s 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 340 m/s]: 
(a) 448 Hz
(b) 350 Hz
(c) 411 Hz
(d) 361 Hz

Answer: A

Question. A train moving at a speed of 220 ms^–1 towards a stationary object, emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is (speed of sound in air is 330 ms^–1)
(a) 5000 Hz
(b) 3500 Hz
(c) 4000 Hz
(d) 3000 Hz

Answer: A

Question. Assertion : The fundemental frequency of an open organ pipe increases as the temperature is increased.
Reason : As the temperature increses, the velocity of sound increases more rapidly than length of the pipe.
(a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion
(b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion
(c) If Assertion is correct but Reason is incorrect
(d) If both the Assertion and Reason are incorrect.

Answer: A

Question.  A sonometer wire resonates with a given tuning fork forming standing waves with five antinodes between the two bridges when a mass of 9 kg is suspended from the wire. When this mass is replaced by a mass M, the wire resonates with the same tuning fork forming three antinodes for the same positions of the bridges. The value of M is
(a) 25 kg
(b) 5 kg
(c) 12.5 kg
(d) 1/25 kg

Answer: A

Question.  A tuning fork of frequency 392 Hz, resonates with 50 cm length of a string under tension (T). If length of the string is decreased by 2%, keeping the tension constant, the number of beats heard when the string and the tuning fork made to vibrate simultaneously is :
(a) 4
(b) 6
(c) 8
(d) 12

Answer: A

Question.  A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 27°C two successive resonances are produced at 20 cm and 73 cm of column length. If the frequency of the tuning fork is 320 Hz, the velocity of sound in air at 27°C is
(a) 339 m/s
(b) 300 m/s
(c) 350 m/s
(d) 330 m/s

Answer: A

Question.  The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe. If the length of the closed organ pipe is 20 cm, the length of the open organ pipe is
(a) 13.2 cm
(b) 8 cm
(c) 16 cm
(d) 12.5 cm

Answer: A

Question. Vibrations are produced in a vertical tube of length 150cm closed at one end by a tuning fork of frequency 340Hz. Now water is filled slowly in the tube. If the speed of sound in air is 340 m/s then the minimum height of water required for resonance is
(a) 25cm
(b) 50cm
(c) 75cm
(d) 90cm

Answer: A

Question.  A granite rod of 60 cm length is clamped at its middle point and is set into longitudinal vibrations. The density of granite is 2.7 × 10³ kg/m³ and its Young's modulus is 9.27×1010 Pa. What will be the fundamental frequency of the longitudinal vibrations? 
(a) 5 kHz
(b) 2.5 kHz
(c) 10 kHz
(d) 7.5 kHz

Answer: A

Question. The wavelength of two waves are 50 and 51 cm respectively. If the temperature of the room is 20°C then what will be the number of beats produced per second by these waves, when the speed of sound at 0°C is 332 m/s?
(a) 14
(b) 24
(c) 10
(d) none of these

Answer: A

Question. 10 forks are arranged in increasing order of frequency in such a way that any two nearest tuning forks produce 4 beats/sec. The highest frequency is twice of the lowest. Possible highest and the lowest frequencies (in Hz) are
(a) 72 and 36
(b) 100 and 50
(c) 80 and 40
(d) 44 and 22

Answer: A

Question.  The total length of a sonometer wire between fixed ends is 110 cm. Two bridges are placed to divide the length of wire in ratio 6 : 3 : 2. The tension in the wire is 400 N and the mass per unit length is 0.01 kg/m. What is the minimum common frequency with which three parts can vibrate?
(a) 1000 Hz
(b) 166 Hz
(c) 1100 Hz
(d) 100 Hz

Answer: A

Question.  A uniform tube of length 60.5 cm is held vertically with its lower end dipped in water. A sound source of frequency 500 Hz sends sound waves into the tube. When the length of tube above water is 16 cm and again when it is 50 cm, the tube resonates with the source of sound. Two lowest  frequencies (in Hz), to which tube will resonate when it is taken out of water, are (approximately).
(a) 272, 544
(b) 276, 552
(c) 281, 843
(d) 281, 562

Answer: A

Question.  While measuring the speed of sound by performing a resonance column experiment, a student gets the first resonance condition at a column length of 18 cm during winter. Repeating the same experiment during summer, she measures the column length to be x cm for the second resonance. Then
(a) x > 54
(b) 36 > x > 18
(c) 18 > x
(d) 54 > x > 36

Answer: A

Question.  An earthquake generates both transverse (S) and longitudinal (P) sound waves in the earth. The speed of S waves in about 4.5 km/s and that of P waves is about 8.0 km/s. A seismograph records P and S waves from an earthquake. The first P wave arrives 4.0  min. before the first S wave. The epicenter of the earthquake is located at a distance about
(a) 2500 km
(b) 5000 km
(c) 250 km
(d) 25 km

Answer: A

Question.  In a standing wave experiment, a 1.2 kg horizontal rope is fixed in place at its two ends (x = 0 and x = 2.0 m) and made to oscillate up and down in the fundamental mode, at frequency 5.0 Hz. At t = 0, the point at x = 1.0 m has zero displacement and is moving upward in the positive direction of y axis with a transverse velocity 3.14 m/s.
(a) 240 N
(b) 120 N
(c) 100 N
(d) 60 N

Answer: A

Question.  A siren is fitted on a car going towards a vertical wall at a speed of 36 km/hr. A person standing on the ground behind the car, listens to the siren sound coming directly from the source as well as that coming after reflection from the wall. The apparent frequency of the wave coming directly from the siren to the person and coming after reflection respectively are (Take the speed of sound to be 340 m/s.)
(a) 486 Hz, 515 Hz
(b) 490 Hz, 510 Hz
(c) 515 Hz, 486 Hz
(d) 510 Hz, 490 Hz

Answer: A

Question.  Two waves of wavelengths 99 cm and 100 cm both travelling with velocity 396 m/s are made to interfere. The number of beats produced by them per second is
(a) None of these
(b) 1
(c) 2
(d) 8

Answer: A

Question. Two similar open organ pipe of length 50 cm and 50.5 cm produce 3 beats per second when sounded together. The velocity of sound in air is
(a) 303 m/s
(b) 151.5 m/s
(c) Both
(d) None of these

Answer: A