1. A person in a parked car sounds the hom. The frcquency of the horn\'s sound i
ID: 1865592 • Letter: 1
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1. A person in a parked car sounds the hom. The frcquency of the horn's sound is 480 Hz, A driver in an approaching car measures the frequency of the hom's sound as 515 Hz. What is the speed of the approaching car? ( Use 343 m/s for the speed of sound.) A) 23.9ms B) 74.16 m/s C) 25.01 m/s D) 37.2 m/s E) 34.224 m's 515?4SO 2. A 350 Hz siren is moving at 50 fi's toward a person running away from it at 25 fis. What pitch does the person hear? (Vsound 1100 f/s) A) 175 Hz B) 70 Hz C) 358.3 Hz D) 875 Hz E) 700 Hz 3. If the distance between a point sound source and a dB detector is increased by a factor of 4, what will be the reduction in intensity level? A) 12.04N B) 14.472N C) 11.88 N D) 3.96 N E) 4.87 N 4. A 36 gm cube of ice, initially at 0° C is dropped into 160 gm of water in a 80 gm aluminum container, both initily at 45° C. What is the final equilibrium temperature? (Specific heat for aluminum is 0.215 cal/gm-Co and L -80 cal/gm.) A) 27.54 °C B) 21.6°C C) 4.1472 °C D) 10.3 °C E 23.89 °C 5. A very loud train whistle has an acoustic power output of 80 watts. If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 105 meters from the train? (1.-10-12 wattsm A) 82.4 dB B) 87.62 dB C) 157.92 dB D) 48.96 dB E) 81.6 dBExplanation / Answer
1.
Vs = speed of source car = 0 m/s
VL = speed of listener car = ?
V = speed of sound = 343 m/s
f' = apparent frequency = 515 Hz
f = actual frequency = 480 Hz
the listener is approaching the source at rest , hence the apparent frequency is given as
f' = (V + VL) f/(V - Vs)
inserting the values
515 = (343 + VL) (480)/(343 - 0)
VL = 25.01 m/s
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