Two simple pendulums whose lengths are 100 cm and 121 cm are suspended side by side. Their bobs are pulled together and then released. After how many minimum oscillations of the longer pendulum, will the two be in phase

• 11

• 10

• 21

• 20

A light source approaches the observer with a velocity of 0.5 c. Doppler's shift for a light of wavelength 5500 Å is:

• 616 Å

• 1833 Å

• 5500 Å

• 6160 Å

A train approaches a stationary observer, the velocity of the train being 1/20 of the velocity of sound. A sharp blast is blown with the whistle of the engine at equal intervals of a second. The interval between the successive blasts as heard by the observer?

• 1/20 sec

• 1/20 min

• 19/20 sec

• 19/20 min

Which of the following equations represents a wave travelling along y-axis?

• y = A sin (x - ωt)

• x = A sin(ky - ωt)

• y = A sin(ky) cosωt

• y = A cos(ky)sinωt

A closed organ pipe and an open organ pipe are tuned to the same fundamental frequency. What is the ratio of their lengths?

• 1 : 2

• 2 : 1

• 2 : 3

• 4 : 3

In a sinusoidal wave, the time required for a particular point to move from maximum displacement to zero displacement is 0.17 sec. The frequency of the wave is :

• 1.47 Hz

• 2.94 Hz

• 0.73 Hz

• 0.36 Hz

When sound waves travel from air to water, which one of the following remains constant?

• Time period

• Frequency

• Velocity

• Wavelength

An organ pipe, opened at both ends, has fundamental frequency of 30 Hz. If one of its ends is closed, then fundamental frequency will be :

• 15 Hz

• 30 Hz

• 45 Hz

• 60 Hz

109.

A stationary police car sounds a siren with a frequency of 990 Hz. If the speed of sound is 30 m/s, an observer, driving towards the car with a speed of 33 m/s, will hear a frequency of

• 891 Hz

• 900 Hz

• 1089 Hz

• 1100 Hz

A wave travelling along positive x-axis is given by y=A sin (ωt -kx). If it is reflected from rigid boundary such that 80% amplitude is reflected then equation of reflected wave is

• y = A sin(ωt - kx)

• y = - 0.8 A sin(ωt + kx)

• y = 0.8 A sin(ωt + kx)

• y=A sin(ωt + 0.8 kx)