131.

A speeding motorcyclist sees traffic jam ahead of him. He slows down to 36 km/hr. He finds that traffic has eased and a car moving ahead of him at 18 km/hr is honking at a frequency of 1392 Hz. If the speed of sound is 343 m/s, the frequency of the honk as heard by him will be,

• 1332 Hz

• 1372 Hz

• 1412 Hz

• 1412 Hz

Two waves are represented by the equations, m where x is in metre and t in second. The phase difference between them is

• 1.25 rad

• 1.57 rad

• 0.57 rad

• 0.57 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.

• increases by a factor 20

• increases by a factor 10

• decreases by a factor 20

• decreases by a factor 20

Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively illuminate a metallic surface whose work function is 0.5 eV successively. Ratio of maximum speeds of emitted electrons will be

• 1:2

• 1:4

• 1:5

• 1:5

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 ms^-1 at an angle of 60^o with the source observer is at rest. the apparent frequency observed by the observer (velocity of sound in air 330 ms^-1) is 

• 100 Hz

• 103 Hz

• 106 Hz

• 106 Hz

A transverse wave os represented by y = A sin (ωt - kx). For what value of the wavelength is the wave velocity equal to the maximum particle velocity?

• π A /2

•  π A

• 2πA

• 2πA

A tuning fork of frequency 512 Hz makes 4 beats/s with the vibrating string of a piano. The beat frequency decreases to 2 beats/s when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was.

• 510 Hz

• 514 Hz

• 516 Hz

• 516 Hz

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 ms^-1 and it is noted that 5 complete waves fit in 4 m length of the string. The equation describing the wave is

• y = (0.02) m sin (7.85 x +1005t)

• y = (0.02) m sin (15.7 x -2010t)

• y = (0.02) m sin (15.7 x + 2010t)

• y = (0.02) m sin (15.7 x + 2010t)

The driver of a car travelling with speed 30 ms^-1 towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 ms^-1, the frequency of reflected sound as heard by driver is

• 550 Hz

• 555.5 Hz

• 720 Hz

• 720 Hz

The wave described by y = 0.25 sin (10 π x -2 πt), where x and y are in metre and t in second, is a wave travelling along the 

• - ve x direction with frequency 1 Hz

• +ve x direction with frequency π  Hz and wavelength λ = 0.2 m

• +ve x direction with frequency 1 Hz and wavelength λ = 0.2 m

• +ve x direction with frequency 1 Hz and wavelength λ = 0.2 m