Question

Two trains , one coming toards and another going away from an observer both at 4 m/s produce a whistle simultaneously of frequency 300 Hz . find the number of beats produced approximately $(V_{sound}=332m/s)$

• A. 5
• B. 6
• C. 7
• D. 12

Answer 1

Answer: (C)

7

$Beats=f_1-f_2$

here, $f_1=f_{whistle}\times \left(\frac{V_{sound}}{V_{sound}-V_{source}}\right)=300\times \frac{332}{332-4}=303.65Hz$

$f_2=f_{whistle}\times \left(\frac{V_{sound}}{V_{sound}-V_{source}}\right)=300\times \frac{332}{332+4}=296.42Hz$

$Beats=f_1-f_2=303.65-296.42=7.22Hz\approx 7Hz$