KVPY SB SX Exam 2011 Question Paper

Question : 28 of 120

Marks: +1, -0

A speaker emits a sound wave of frequency

f_o

. When it moves towards a stationary observer with speed u. the observer measures a frequency

f_1

. If the speaker is stationary, and the observer moves towards it with speed it. the measured frequency is

f _2

. Then

Solution:

\table \S_{●}→u,,_{●}\O

f_1={f_0[v]}/{v-u}

\table \S_{●} ,,v ← _{●}\O

f_2=f_0[v+u]/v

f_2-f_1=f_0({u+v}/v-v/{v-u})

f_2-f_1={-u^2f_0}/{(v)(v-u)}=-\ve

∴f_1 > f_2

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