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Mechanical Properties Of Fluids

Question
CBSEENPH11019356

Write the differential equation for damped forced oscillations and discuss the conditions of resonance.

Solution
The differential equation for damped forced oscillation is, 
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Solution of the above differential equation is,
space space space space space space space space space space space space space straight y equals straight A space cos open square brackets ωt plus straight ϕ close square brackets space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis

where comma
space space space space space straight A space equals space fraction numerator straight f subscript straight omicron over denominator straight m square root of begin display style fraction numerator straight b squared straight omega squared over denominator straight m squared end fraction end style plus open parentheses straight omega squared plus straight omega subscript straight omicron squared close parentheses squared end root end fraction space space space space space space space space space space... left parenthesis 2 right parenthesis
Resonance is the state of vibration in which the oscillator oscillates with maximum amplitude.
Thus, the condition of resonance is that A should be maximum.
Therefore denominator of equation (2) should be minimum. 
straight i. straight e. space space space space straight d over dω open parentheses fraction numerator straight b squared straight omega squared over denominator straight m squared end fraction plus left parenthesis straight omega squared minus straight omega subscript 0 squared right parenthesis squared close parentheses equals 0
rightwards double arrow space space space space space space space straight b squared over straight m squared 2 straight omega plus 2 left parenthesis straight omega squared minus straight omega subscript 0 squared right parenthesis 2 straight omega equals 0
rightwards double arrow space space space space space space space straight omega equals square root of straight omega subscript 0 squared minus fraction numerator straight b squared over denominator 2 straight m squared end fraction end root space space space space space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis
Substituting space straight omega in equation (2), we get
straight A subscript max equals fraction numerator straight f subscript 0 over denominator straight b square root of straight omega subscript 0 squared minus begin display style fraction numerator straight b squared over denominator 4 straight m squared end fraction end style end root end fraction space space space space space space space space space space... left parenthesis 4 right parenthesis 
The oscillator is in the state of resonance if the frequency of external force is given by, 
            space space space square root of straight w subscript 0 squared minus fraction numerator straight b squared over denominator 2 straight m squared end fraction end root