A man beats a drum at a certain distance from a mountain. He slowly increases the rate of being and finds that the echo is not heard distinctly when the drum beating is at the rate of 40 per minute. He moves by 80 m towards the mountain and finds that the echo is again not heard distinctly when the rate of beating of the drum is 1 per second. What is the original distance of the man from the mountain?


Correct option is

240 m


The echo is not heard distinctly when the echo and the next beat fall on the ear simultaneously, i.e., time per beat = time taken by the reflected beat to reach the man.

This gives      d = 240 m.



Two sources A and B are sounding notes of frequency 680 Hz. A listener moves from A to B with a constant velocity u. If the speed of sound is 340 m/s, what must be the value of u so that he hears 10 beats per sec?


A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m/s. Velocity of sound is 330 m/s. The number of beats per second heard by an observer standing between the source and the wall is nearly:


A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m/s. The velocity of sound is 330 m/s. The number of beats heard by an observer moving along with the sounding object is:


A train has just completed a U-curve in a track which is a semi-circle. The engine is at the forward end of the semicircular part of the track while the last carriage is at the rear end of the semicircular track. The driver blows a whistle of frequency 200 Hz. Velocity of sound is 340 m/s. Then the apparent frequency as observed by a passenger in the middle of the train, when the speed of the train is 30 m/s, is:


A mass m is suspended separately from two springs of constants k1 andk2. Their time periods are found to be T1 and T2 respectively. If the same mass is suspended from the two springs connected in series, then the time period of the combination will be:


Two particles are executing SHM of same amplitude and frequency along the same straight line path. They pass each other when going in opposite directions, each time their displacement is half of their amplitude. What is the phase difference between them? 



The figure below shows the wave y = A sin (ωt – kx), at any instant travelling in the +ve x-direction. What is the slope of the curve at B?



What is the ratio of the speed of sound in neon and water vapours at the same temperature? It is nearest to:


In case of the mechanical longitudinal wave y = A sin (ωt – kx) in air (density ρ), what is the relation between displacement amplitude and pressure amplitude?


In an experiment, it was found that a tuning fork and a sono-meter emitting its fundamental note, gave 5 beats per second both when the length of the wire was 1 metre and 1.05 metre. The velocity of transverse waves in the sono-meter wire is: