Posted by ashu on .
to an observer the pitch of the stationary source of the sound appears to be reduced by 20% if speed of sound is 340m/s then sped and direction of 5he observer is
options
1.68 m/s away from the observer
2.96 m/s away from the observer

physics 
Elena,
{f(observed)  f(source)}/f(observed) = 20/100, u = 340 m/s
At source approaching
f(observed) = [v/(vu)] •f(source),
v =[f(obs)f(sour)] •u/ f(obs) = 20% •340/100%= 68 m/s.