The intensity of sound increases at night due to

When an aeroplane attains a speed higher than the velocity of sound in air,a loud bang is heard. This is because

An engine approaches a hill with a constant speed. When it is at a distance of $0.9 \ km$,it blows a whistle,and the echo is heard by the driver after $5 \ s$. If the speed of sound in air is $330 \ m/s$,the speed of the engine is .... $m/s$.

Does an oscillating source always produce sound waves?

The figure below shows pressure variation in two different sound waves in air with time at a given position. Both the figures are drawn to the same scale. Which of the following statements is true?

$A$ plane wave of sound traveling in air is incident upon a plane surface of a liquid. The angle of incidence is $60^{\circ}$. The speed of sound in air is $300 \ m/s$ and in the liquid it is $600 \ m/s$. Assume Snell's law to be valid for sound waves.