-a sound wave causes the density at a place in air to oscillate 600 ties in 30 seconds. Find the time period and frequency of the sound wave.

-a sound wave produces 20 crests and 20 troughs in 0.2 seconds. find the frequency of the wave.

-a person is sitting 200 m away from a 20Hz sound source. what is the time interal at which successive compressions from the source reaching?

(1)-a sound wave causes the density at a place in air to oscillate 600 ties in 30 seconds. Find the time period and frequency of the sound wave.

As frequency is the no of oscillations per sec and time period is the reciprocal of frequency:

v = 600/30 = 20 Hz

T = 1/v = 0.05 second. 

(2)-a sound wave produces 20 crests and 20 troughs in 0.2 seconds. find the frequency of the wave.

1 crest and 1 trough complete 1 wave. So, 20 crests and 20 troughs complete 20 waves.

In 0.2 s we have 20 complete waves

So, in 1 s we have, f = 20/0.2 = 100 Hz. This is the frequency.

Time period is, T = 1/f = 1/100 = 0.01 s

Similarly you can attempt the last question.