A girl stands 160m away from a high wall and claps her hands at a steady rate so that each clap coincides with the echo of the one before.If she makes 60 claps in one minute,What value of speed does this give ?
(B)If she moves 40m closer to the wall,she finds the clapping rate has become 80 per minute.What values does these measurements give for the speed of sound?
(C)If she moves again and finds the clapping rate becomes 30 per minute,how far is she from wall If the speed of the Sound is the value you find in A?

solutions:
A. wavelength=160m
frequency=60 claps÷60 claps=1H z
velocity of sound=frequency X wavelength
=1x 160=160m/s

B. since she moves 40m closer,wavelength=160m minus 40m=120m
f=8O÷ 60=1.33Hz
V=120×1.33=159.6m/s

(C).F = 30÷ 60=0.5Hz
but F=1÷T    ⇒T=1÷F  ⇒ 1÷0.5=2s
wavelength=speed of wave÷frequency ⇒ wavelength=v÷f
⇒ 160÷2=80m