Making a Sound Lens

A person standing on the edge of a well throws a stone vertically upwards with an initial velocity 5ms^(-1) . The stone gone up, comes down and falls in the well making a sound. If the person hears the sound 3 seconds after throwing the the depth of water (neglect time travel for the sound and take g=10ms^(-2) )

An aeroplane flying horizontally makes a sound when its angle of elevation w.r.t a person on ground is theta . But the sound reached the person, when the aeroplane was just over him. Find the mach.no. of the aeroplane. Also find its speed if speed of sound in air is 'v'_(s) .

Under what condition, a concave lens can make a real image.

What are overtones and harmonics ? The presence of which makes a sound musical ?

Two friends blow two whistles at the same time. The first whistle makes a sound whose frequency is twice that of the sound made by the other whistle. Which sound will reach you first ?

Statement-1 : A balloon filled with CO_(2) gas acts as a coverging lens for a sound wave Statement-2 : Sound waves travel faster in air than in CO_(2)

What is a lens? Distinguish between a convex lens and a concave lens. Which of the two is a converging lens: convex and lens or concave lens?