Question

A source and an observer moves away from each other, with a velocity of 15 m/s with respect to ground. If observer finds the frequency of sound coming from source as 1950 Hz. Then actual frequency of source will be (velocity of sound = 340 m/s):

• A. 1785 Hz
• B. 1968 Hz
• C. 2130 Hz
• D. 2148 Hz

Answer 1

Answer: (C)

Apparent frequency $n=n\frac{\upsilon -{\upsilon }_0}{\upsilon +{\upsilon }_s}$ where, ${\upsilon }_0$ = speed of observer ${\upsilon }_s$ = speed of source, $\upsilon$ = speed of sound, n = actual frequency $\therefore$ $1950=n\frac{340-15}{340+15}$ $n=\frac{1950\times 355}{325}=2130Hz$