Question

A source $S$ of frequency $f_o$ and an observer $O,$ moving with speeds $V_1$ and $V_2$ respectively, are moving away from each other. When they are separated by distance $a(t=0),$ a pulse is emitted by the source. This pulse is received by $O$ at time $t_1$ then $t_1$, is equal to

• A. $\frac{a}{V_S+V_2}$
• B. $\frac{a}{V_l+V_S}$
• C. $\frac{a}{V_S-V_2}$
• D. $\frac{a}{V_l+V_2+V_S}$

Answer 1

Answer: (C)

$\frac{a}{V_S-V_2}$

Here one point that we should keep in mind is Velocity of Source won't affect the speed of sound
Now since sound is set in motion with speed Vs and receiver i.e observer is also moving so relative velocity will be $=Vs-V2$

So time to travel Distance a will be $=a/\left(Relativevelocity\right)=a/(Vs-V2)$

Hence solved