When an observer moves towards a stationary source with certain velocity, he observes an apparent frequency…
When an observer moves towards a stationary source with certain velocity, he observes an apparent frequency $f$. When it moves away from the source with same velocity, the observed frequency is $0.8 f$. If the velocity of sound is $v$, then the speed of the observer is
$\frac{v}{4}$
$\frac{v}{8}$
$\frac{v}{9}$
None of these
Solution
Suppose $f_o$ be the actual frequency. Then,
$f = f_o \left(\frac{v + v_o}{v}\right)$ and $0.8 f = f_o \left(\frac{v - v_o}{v}\right)$
Solving these two equations, we get
$v_o = \frac{v}{9}$