Waves

The frequency of the second overtone of the open pipe is equal to the frequency of the first overtone of the closed pipe. The ratio of the lengths of the open pipe and the closed pipe is

• 2 : 1

• 1 : 2

• 1 : 3

• 3 : 1

A person with vibrating tuning fork of frequency 338 Hz is moving towards a vertical wall with a speed of 2 ms^-1 . Velocity of sound in air is 340 ms^-1. The number of beats heard by that person per second is

• 2

• 4

• 6

• 8

A metallic wire of 1 m length has a mass of 10 x 10^-3 kg. If a tension of 100 N is applied to a wire, what is the speed of transverse wave ?

• 100 ms^-1

• 10 ms^-1

• 200 ms^-1

• 0.1 ms^-1

A trainis approaching towards a platform with a speed of 10 ms^-1 while blowing a whistle of frequency 340 Hz. What is the frequency of whistle heard by a stationary observer on the platform ? Given speed of sound = 340 ms^-1.

• 330 Hz

• 350 Hz

• 340 Hz

• 360 Hz

When two tuning forks A and B are sounded together, 4 beats per second are heard. The frequency of the fork B is 348 Hz. When one of the prongs of the fork A is filled and sounded with B, the beat frequency increases, then the frequency of the fork A is

• 379 Hz

• 380 Hz

• 389 Hz

• 388 Hz

A source of sound is moving with a velocity of 50 ms^-1 towards a stationary observer. The observer measures the frequency of sound as 500 Hz. The apparent frequency of sound as heard by the observer when source is moving away from him with the same speed is (Speed of sound at room temperature is 350 ms^-1)

• 400 Hz

• 666 Hz

• 375 Hz

• 177.5 Hz

The waves set up in a closed pipe are

• longitudinal and progressive

• transverse and progressive

• transverse and stationary

• longitudinal and stationary

A racing car moving towards a cliff, sounds its horn. The driver observes that the sound reflected from the cliff has a pitch one octave higher than the actual sound of the horn. If v is the velocity of sound, then the velocity of the car is

• v/2

• $\mathrm{v}/\sqrt{2}$

• v/4

• v/3

A railway engine whistling at a constant frequency moves with a constant speed. It goes past a stationary observer beside the railway track. Which of the following graphs best represent the variation of frequency of the sound n heard by the observer with the time t ?

The tension of a stretched string is increased by 69 %. In order to keep its frequency of vibration constant, its length must be increased by

• 30 %

• 20 %

• 69 %

• $\sqrt{69} \%$