Question

A source and an observer move away from each other with a velocity of 10 m/s with respect to ground.If the observer finds the frequency of sound coming from the source as 1950 Hz, then actual frequency of the source is (velocity of sound in air =340 m/s): a)2132 Hz. b)1950 Hz. c)2486 Hz. d)2068 Hz.

Answer 1

Answer on Question #38042, Physics, Other

Question:

A source and an observer move away from each other with a velocity of $10\mathrm{m/s}$ with respect to ground. If the observer finds the frequency of sound coming from the source as $1950\mathrm{Hz}$, then actual frequency of the source is (velocity of sound in airt =340m/s):

a) 2132Hz

b) 1950Hz

c) 2486Hz

d) 2068Hz

Answer:

$$F = F _ {0} \frac {c + v _ {R}}{c + v _ {s}}$$

F - observed frequency;

$F_{0}$ - emitted frequency;

$c$ - the velocity of waves in the medium;

$v_{R}$ - the velocity of the observer relative to the medium $(\ll + v_{R}) \gg$ - observer is moving towards the source, $\ll - v_{R} \gg$ - observer is moving from the source);

$v_{s}$ - the velocity of the source relative to the medium $((\ll + v_{s}) \gg$ - source is moving from the observer, $\ll - v_{s} \gg$ - source is moving to the source);

→

$$F _ {0} = F \frac {c + v _ {s}}{c + v _ {R}} = 1 9 5 0 * \frac {3 4 0 + 1 0}{3 4 0 - 1 0} = 2 0 6 8 H z$$

Answer: d)2068Hz