Question

PHYSICS!! PLEASE HELP! MY TEACHER GIVES US THE ANSWERS BUT WE HAVE TO SHOW ALL WORK! PLEASE SHOW WORK FOR EACH PART OF THE QUESTION! THANK YOU!!

4) A bat is flitting around a cave navigating via ultrasonic bleeps. Assume that the sound emission frequency of the bat is 39,000 Hz. During one fast swoop directly toward a flat wall surface, the bat is moving at 0.025 times the speed of sound in air. The temperature in the cave is 18.9°C a) What is the frequency detected at the wall? (Ans: fD- 40,000 Hz) b) What is the frequency detected by the bat? (Ans: fD- 41,001 Hz)

Answer 1

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First of all,we will find speed of sound for given temperature

v = 331m/s + 0.6m/s/C * T

v = 331 + 0.6*18.9

v = 342.34 m/s

Now, we will use Doppler's equation

(a) Here bat is source and wall is observer

f' = (v / v - v_s)f

v = Velocity of sound or light in medium,
f = Real frequency,
f' = Apparent frequency

v_s = speed of source

f' = (342.34 / 342.34 - 0.025*342.34 )39,000

f' = 40000 Hz

Therefore, frequency detected by wall is 40000 Hz

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(b) Now, the frequency which is reflected off the wall is caught by bat

so,

f = (342.34 + 0.025 * 342.34 / 342.34 ) * 40000

f = (350.9 / 342.34) * 40000

f = 41001 Hz