MCQ : Sound - 2 - UPSC

Here, distance = 3 km = 3000 m 
Time  = 2 sec 
Therefore, speed= distance / time
=  3000 /2
=  1500 m /s 

Sound is only audible to the average humar ear if the frequencies lie between 20 Hz and 20 kHz. The actual range varies from person to person. Sound waves with frequencies less than 20 Hz are called infrasonic or subsonic and those with frequencies above 20 kHz are called ultrasonic. 

If you have persistence, you continue to do something even though it is difficult or others are against it. 

( As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between  the original sound and the reflected one must be at least 0.1 s. If we take the speed of the sound to be 300 m/s at a given temperature, in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s. )

Reflection of sound is used in many devices. For example ; megaphone, loudspeaker, bulb horn, stethoscope, hearing aid, sound board etc.

Sound  travels faster in soilds than in liquids, and faster in liquids than in gases. This is because the density of solids is higher than that of liquids which means that the particles are closer together.

To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.15

The speed is 330 m / s and the time taken is 5.5 second. Therefore, the distance would be speed * time ⇒ 5.5 * 330 = 1815m