Bats have no eyes,yet they can ascertain the distance,direction,nature,and size of objects. Explain why.

How does the sound produced by a musical instrument reach your ears? Astronauts need radio transmitters to talk to each other on the moon. Why?

Ultrasonic waves are not used in which of the following?

$(a)$ Why are sound waves called mechanical waves? List two practical applications of reflection of these waves.
$(b)$ $A$ stone is dropped from the top of a tower $125 \ m$ high into a pond of water at the base of the tower. When is the splash heard at the top? $(g = 10 \ m s^{-2}$ and speed of sound $= 340 \ m s^{-1})$

Define the following terms and state their $SI$ units:
$(a)$ Wavelength $(b)$ Time period $(c)$ Amplitude.
Establish the relation $V = v \lambda$,where the symbols have their usual meanings.

The bells of a temple are made of large size. It is for