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NEET Sample Paper NEET Sample Test Paper-23

  • question_answer
    A whistle emitting a sound of frequency 440 Hz is tied to a string of 1.5 m length and rotated with an angular velocity of 20 rad/sec in the horizontal plane. Then the range of frequencies heard by an observer stationed at a large distance from the whistle will be: (U = 330 m/s):

    A)  400.0 Hz to 484.0 Hz

    B)  403.3 Hz to 480.0 Hz

    C)  400.0 Hz to 480.0 Hz

    D)  403.3 Hz to 484.0 Hz

    Correct Answer: D

    Solution :

    \[{{f}_{\max }}=\frac{v}{v-{{v}_{s}}}\times {{f}_{0}};\]where, \[{{f}_{0}}=440\,Hz\] Here,\[v=330m/s,\,{{v}_{s}}=r\omega =1.5\times 20=30\,m/s\] Inserting the above values, we get \[{{f}_{\max }}=\frac{330}{330-30}\times 440=484\,Hz\] \[{{f}_{\min }}=\frac{330\times 440}{330-(-30)}=403\,.3Hz\] Hence, the correction option is [d].


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