WAVE MOTION QUIZ-1

Q1. A police car moving at22 ms^(-1), changes a motorcyclist. The police man sounds his horn at 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of the motorcycle, if it is given that he does not observe any beats.

•  0 ms^(-1)
•  33 ms^(-1)
•  11 ms^(-1)
•  22 ms^(-1)

Solution
The motorcyclist observes no beats. So the apparent frequency observed by him from the two sources must be equal. ∴176 ((330-v)/(330-22))=165 ((330+v)/330) Solving this equation we get, v=22ms^(-1)

Q2.A stone is hung in air from a wire which is stretched over a sonometer. The bridges of the sonometer are L cm apart when the wire is in unison with a tuning fork of frequency N. When the stone is completely immersed in water, the length between the bridges is l cm for re-establishing unison, the specific gravity of the material of the stone is

•  (L^2-l^2)/L^2
•  L^2/(L^2-l^2 )
•  L^2/(L^2+l^2 )
•  (L^2+l^2)/L^2

Solution

Q3.  A man standing between two parallel hills, claps his hand and hears successive echoes at regular intervals of 11s. If velocity of sound is 340ms^(-1), then the distance between the hills is

•   100m
•  170 m
•  340 m
•  510 m

Solution

Q4. The disc of a siren containing 60 holes rotates at a constant speed of 360 rpm. The emitted sound is in unison with a tuning fork of frequency

•  10 Hz
•  60 Hz
•  216 Hz
•  360 Hz

Solution
Speed =360 revolutions per min =360/60 revolutions per sec=6 ∴ frequency =6×60=360

Q5.A wire of density 9×〖10〗^3 kgm^(-3) is stretched between two clamps 1m part and is subjected to an extension of4.9×〖10〗^(-4) m. The lowest frequency of transverse vibration in the wire is Y=9×〖10〗^10 Nm^(-2))

•  35 Hz
•  30 Hz
•  25 Hz
•  40 Hz

Solution
 

Q6. A piston fitted in cylindrical pipe is pulled as shown in the figure. A tuning fork is sounded at open end and loudest sound is heard at open length 13cm, 41 cm and 69 cm, the frequency of tuning fork if velocity of sound is 350ms^(-1)is

•  1250 Hz
•  625 Hz
• 417 Hz
•  715 Hz

Solution

Q7.Quality of a musical note depends on

•  Velocity of sound in the medium
•  Fundamental frequency
•  Harmonics present
•  Amplitude of the wave

Solution
The quality of sound depends upon the number of harmonics present. Due to different number of harmonics present in two sounds, the shape of the resultant wave is also different

Q8.A 5.5 m length of string has a mass of 0.035 kg. If the tension in the string is 77 N, the speed of a wave on the string is

•  165m^(-1)
•  110ms^(-1)
•  77ms^(-1)
•  102ms^(-1)

Solution
m=0.035/5.5 kg m^(-1),T=77N v=√(T/m)=√((77×5.5)/0.035)=110ms^(-1)

Q9.When an aeroplane attains a speed higher than the velocity of sound in air, a loud bang is heard. This is because

•  It explodes
•  The normal engine noises undergo a Doppler shift to generate the bang
•  Its wings vibrate so violently that the bang is heard
•  It produces a shock wave which is received as the bang

Solution
D

Q10. A tuning fork of frequency 200 Hz is in unison with a sonometer wire. The number of beats heard per second when the tension is increased by 1% is

•  2
•  1
•  1/2
• 4

Solution