26.A locomotive approaching a crossiing at a speed of 80miles/hr,sounds a whistle of frequency 400HZ when 1 mile from the crossing.There is no wind,and the speed of the sound in air is 0.200miles/sec.what frequency is heard by an observer 0.60miles from the crossing on the straight road which crosses the rail road at right angles?

In the above figure, s is the position of locomotive and O is the position of observer when the locomotive whistles.Angle SAO=900AO=0.6 milesSA=1.0 mileComponent of vs along SO,v'=vscosθFrom the figure, we havecosθ=SASO=1.01.02+0.62=0.857Speed of sound, v=0.200 mile/secSpeed of locomotive, vs=80 mile/hour=803600mile/sec=0.022 mile/secTherefore,v'=0.022×0.857=0.019 mile/secThe apparent frequency when source is in motion is given by,f=0.200.20-0.019×400=442 Hz

  • 24
What are you looking for?