1. A friend of yours is loudly singing a single note at 400 Hz while driving toward you at 25.0 m/s on a day when the speed of sound is 340 m/s. a. What frequency do you hear? b. What frequency does your friend hear if you suddenly start singing at 400 Hz? c. Once your friend reaches you, and you are next to each other (essentially at the same location) and not moving, your friend sings 400 Hz. You are also singing. If you hear 3 beats per second, what frequency are you singing?

Question

Gracie George

Physics

30 April, 18:09

1. A friend of yours is loudly singing a single note at 400 Hz while driving toward you at 25.0 m/s on a day when the speed of sound is 340 m/s. a. What frequency do you hear? b. What frequency does your friend hear if you suddenly start singing at 400 Hz? c. Once your friend reaches you, and you are next to each other (essentially at the same location) and not moving, your friend sings 400 Hz. You are also singing. If you hear 3 beats per second, what frequency are you singing?

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Answers (1)

Know the Answer?

Erick Larson · Answer 1

a) 431 Hz

b) 429 Hz

c) 403 Hz

Explanation:

The frequency you heard is calculated using the relation

f = f (s) / [1 - (v (s) / v) ]

f = 400 / [1 - 25/343]

f = 400 / (1 - 0.0729)

f = 400 / 0.9271

f = 431.5 Hz

The frequency your friend starts hearing is

f = f (s) * [1 + (v (s) / v) ]

f = 400 * [1 + 25/343]

f = 400 * (1 + 0.0729)

f = 400 * 1.0729

f = 429.2 Hz

when you're next to each other and you are hearing 3 beats per second. The frequency you're singing is 400 + 3 Hz

403 Hz