A train moving at a speed of 220 ${\mathrm{ms}}^{-1}$ 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 an echo. The frequency of the echo as detected by the driver of the train is
(speed of sound in air is 330 ${\mathrm{ms}}^{-1}$)
1. 3500Hz
2. 4000Hz
3. 5000Hz
4. 3000Hz

Two waves are represented by the equations ${\mathrm{y}}_1=\mathrm{a} \sin (\mathrm{\omega t}+\mathrm{kx}+0.57)\mathrm{m}$ and ${\mathrm{y}}_2=\mathrm{a} \cos (\mathrm{\omega t}+\mathrm{kx})\mathrm{m}$, where x is in metre and t in second. The phase difference between them is?

(1) 1.25 rad

(2) 1.57 rad

(3) 0.57 rad

(4) 1.0 rad

Sound waves travel at 350 m/s through a warm 

air and at 3500 m/s through brass. The wavelength

of a 700 Hz acoustic wave as it enters brass from 

warm air :

(1) increases by factor 20

(2) increases by factor 10

(3) decreases by factor 20

(4) decreases by factor 10

Two particles are oscillating along two close parallel straight lines side by side, with the same frequency and amplitudes. They pass each other, moving in opposite directions when their displacement is half of the amplitude. The mean positions of the two particles lie on a straight line perpendicular to the paths of the two particles. The phase difference is :

(1)zero                                 

(2)$\frac{2\mathrm{\pi }}{3}$

(3)$\mathrm{\pi }$                                     

(4)$\frac{\mathrm{\pi }}{6}$

A transverse wave is represented by y=$A \sin \left(\omega t-kx\right).$ For what value of the wavelength is the wave velocity equal to the maximum particle velocity?

(1) $\mathrm{\pi } \mathrm{A}/2$                                           

(2) $\mathrm{\pi } \mathrm{A}$

(3) $2 \mathrm{\pi } \mathrm{A}$                                           

(4) A

A wave in a string has an amplitude of 2 cm. The wave travels in the +ve direction of x-axis with a speed of $128 {\mathrm{ms}}^{-1}$ and it is noted that 5 complete waves fit in 4 m length of the string. The equation describing the wave is :

(1) $y=\left(0.02\right)\mathrm{m} \sin \left(7.85\mathrm{x} +1005\mathit{ }t \right)$

(2) $y=\left(0.02\right)\mathrm{m} \sin \left(15.7\mathrm{x} -2010\mathit{ }t \right)$

(3) $y=\left(0.02\right)\mathrm{m} \sin \left(15.7\mathrm{x} +2010\mathit{ }t \right)$

(4) $y=\left(0.02\right)\mathrm{m} \sin \left(7.85\mathrm{x} -1005\mathit{ }t \right)$

Each of the two strings of length 51.6 cm and 49.1 cm are tensioned separately by 20N force. Mass per unit length of both the strings is same and equal to 1 $g{m}^{-1}$When both the strings vibrate simultaneously the number of beats is :

1. 5                                                   

2. 7

3. 8                                                   

4. 3

Two periodic waves of intensities $I_1 and I_2$ pass through a region at the same time in the same direction. The sum of the maximum and  minimum intensities is :

(1) $I_1+I_2$

(2) ${\left(\sqrt{I_1}+\sqrt{I_2}\right)}^2$

(3)${\left(\sqrt{I_1}-\sqrt{I_2}\right)}^2$

(4) $2 \left(I_1+I_2\right)$