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Mechanical Properties Of Fluids

Question
CBSEENPH11020288

The amplitude of a damped oscillator decreases to 0.9 times its original magnitude is 5s. In another 10s it will decrease to α times its original magnitude, where α equals

  • 0.7

  • 0.81

  • 0.729

  • 0.6

Solution

C.

0.729

Amplitude of damped oscillator
straight A space equals space straight A subscript 0 straight e to the power of negative fraction numerator bt over denominator 2 straight m end fraction end exponent
After space 5 straight s comma space space space 0.9 space straight A subscript straight o space equals space straight A subscript straight o straight e to the power of negative fraction numerator straight b left parenthesis 5 right parenthesis over denominator 2 straight m end fraction end exponent space space.. space left parenthesis straight i right parenthesis space
After space 10 space more space second comma
straight A space equals space straight A subscript straight o straight e to the power of negative straight b fraction numerator 15 over denominator 2 straight m end fraction end exponent
straight A space equals space straight A subscript straight o open parentheses straight e to the power of negative straight b fraction numerator 15 over denominator 2 straight m end fraction end exponent close parentheses cubed space space... space left parenthesis ii right parenthesis
From space Eqs. space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis comma
straight A space equals space 0.729 space straight A subscript straight o space equals space αA subscript 0
Hence comma space straight alpha space equals space 0.729