MCQ
When a car is approaching the observer, the frequency of horn is $100 Hz$. After passing the observer, it is $50\,Hz$. If the observer moves with the car, the frequency will be $\frac{ x }{3} Hz$ where $x =.....$
- A$202$
- B$2000$
- C$20$
- ✓$200$
✓
Answer
Correct option: D.
$200$
d
$f_{1}=100=f_{0}\left(\frac{C}{C-V_{5}}\right)$
$f_{1}=100=f_{0}\left(\frac{C}{C-V_{5}}\right)$
$C =$ speed of sound
$V_{S}=$ speed of source
$f_{2}=50=f_{0}\left(\frac{C}{C+V_{5}}\right)$
$\frac{f_{1}}{f_{2}}=2=\frac{C+V_{5}}{C-V_{5}}$
$2 C -2 V _{ s }= C + V _{ s }$
$3 V _{ s }= C$
$V _{ S }=\frac{ C }{3}$
$100= f _{0} \frac{ C }{\frac{2 C }{3}}=\frac{3}{2} f _{0}$
$f _{0}=\frac{200}{3}$
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