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A person standing 345 m from a large wall claps his hands facing the wall. The temperature of air is 25 degree C. Assume the speed of sound in air is 330 m/s at 0 degree C, and increases by 0.6 m/s for every degree rise in temperature. a) What is the speed (in m/s) of sound in air at 25 degree C? c) If the person was moving towards the wall at 10 m/s while he clapped, what will be the time (in seconds) after which he hears back the echo? (Give your answers up to 2 decimal places)
Asked by zr150349 | 04 Sep, 2023, 06:44: PM
Expert Answer
Speed of sound in air at 25o C is 
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If the person moving with speed 10 m/s while clapping , then speed of sound towards the wall is ( 345+10 ) m/s = 355 m/s .
Time t1 taken by sound to reach the wall = distance / speed = ( 345 / 355 ) s = 0.972 s
Distance moved by the observer during this time duration t1 is = 10 × 0.972 m = 9.72 m
Distance between the person and wall when the sound started travelling backwards is ( 345 - 9.72 ) m = 335.28 m
Now sound travels backward by speed 345 m/s and person travels forward by speed 10 m/s .
If t2 is time taken by the person to hear the sound that is travelling backwards , then we have
From above expression, we get t2 = 0.944 s
Total time = t1 + t2 = ( 0.972 + 0.944 ) s = 1.916 s
Echo is heard by person after 1.92 s
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