State whether the following statement is true or false: The velocity of sound in air is higher for higher frequencies than for lower frequencies.

Give reasons for the following:
$(a)$ The reverberation time of a hall used for speeches should be very short.
$(b)$ $A$ vibrating body produces sound. However,no sound is heard when a simple pendulum oscillates in air.
$(c)$ Sounds of same loudness and pitch but produced by different musical instruments like a violin and flute are distinguishable.

The audible range for a normal human being is

What is $SONAR$? For what is it used? Explain its working in brief.

Name the two types of mechanical waves.

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?