KVPY SA Exam 2018 Question Paper

Question : 67 of 80

Marks: +1, -0

A person in front of a mountain is beating a drum at the rate of 40 per minute and hears no distinct echo. If the person moves 90 m closer to the mountain, he has to beat the drum at 60 per minute to not hear any distinct echo. The speed of sound is

320 ms $^{–1 }$
340 ms $^{–1 }$
360 ms $^{–1 }$
380 ms $^{–1 }$

Validate

Solution:

60/40={2d}/v

60/60={2(d-90)}/v={2d}/v-180/v

1=3/2-180/v⇒180/v=1/2

V = 360 m/s.

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