chp. 12 #47,48,49 A train is approaching a signal tower at a speed of 40 m/s. Th

Question

chp. 12 #47,48,49

A train is approaching a signal tower at a speed of 40 m/s. The train engineer sounds the 1000 Hz whistle and a switchman in the tower responds by sounding the 1200 Hz siren. The air is still and the speed of sound is 340 m/s. In Situation 12.2, the frequency of the train whistle tone, heard by the switchman, in SI units, is given by: 380/340 times 1000 1000 300/340 times 1000 340/380 times 1000 340/300 times 1000 In Situation 12.2, the frequency of the tower siren tone, heard by the engineer, in SI units, is closest to: 340/380 times 1200 340/300 times 1200 300/340 times 1200 380/340 times 1200 1200 The tension in each of two strings is adjusted so that both vibrate at exactly 819 Hz. The tension in one of the strings is then increased slightly. As a result, six beats per second are heard when both strings vibrate. What is the new frequency of the string that was tightened? 822 Hz 825 Hz 816 Hz 813 Hz

Explanation / Answer

from Doppler effect

while approaching

fL = fs *(V + Vs)/(V+ VL)

fL = 1000*(340+40)/(340+0)

fL = 1000* 380/340

option A it is

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#48 :

while approaching

fL = fs *(V + Vs)/(V+ VL)

fL = 1200*(340+40)/(340+0)

fL = 1200* (340+40)/(340)

fL = 1200* 380/340

option D it is

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# 49:

beat frequency f = fa - fb

fa = f + fb

fa = 819 + 6

fa = 825 Hz

option B it is

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