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Oscillations

Question
CBSEENPH11020485

A particle at the end of a spring executes simple harmonic motion with a period t1, while the corresponding period for another spring is t2. If the period of oscillation with the two springs in series is t, then

  • T = t1 + t2

  • straight T squared space equals space straight t subscript 1 superscript 2 space plus space straight t subscript 2 superscript 2
  • space straight T to the power of negative 1 end exponent space equals straight t subscript 1 superscript negative 1 end superscript space plus straight t subscript 2 superscript negative 1 end superscript
  • space straight T to the power of negative 1 end exponent space equals straight t subscript 1 superscript negative 2 end superscript space plus straight t subscript 2 superscript negative 2 end superscript

Solution

B.

straight T squared space equals space straight t subscript 1 superscript 2 space plus space straight t subscript 2 superscript 2

Time period of spring
straight T space equals space 2 straight pi square root of straight M over straight k end root
k, being the force constant of spring. For first spring and for second spring
we have,
straight T space equals space 2 straight pi square root of straight m over straight k subscript 1 end root space space space....... space left parenthesis straight i right parenthesis

straight T space equals space 2 straight pi square root of straight m over straight k subscript 2 end root space......... space left parenthesis ii right parenthesis
The effective force constant in their series combination is
straight k space equals fraction numerator straight k subscript 1 straight k subscript 2 over denominator straight k subscript 1 plus straight k subscript 2 end fraction
therefore space Time space period space of space combination

straight T space equals space 2 straight pi space square root of open square brackets fraction numerator straight m left parenthesis straight k subscript 1 plus straight k subscript 2 right parenthesis over denominator straight k subscript 1 straight k subscript 2 end fraction close square brackets end root
straight T squared space equals space fraction numerator 4 straight pi squared straight m space left parenthesis straight k subscript 1 plus straight k subscript 2 right parenthesis over denominator straight k subscript 1 straight k subscript 2 end fraction space...... space left parenthesis iii right parenthesis
From space equations space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis comma space we space obtain
straight t subscript 1 superscript 2 space plus space straight t subscript 2 superscript 2 space equals space 4 straight pi squared space open parentheses straight m over straight k subscript 1 space plus straight m over straight k subscript 2 close parentheses
rightwards double arrow straight t subscript 1 superscript 2 space plus space straight t subscript 2 superscript 2 space equals space 4 straight pi squared straight m space open parentheses 1 over straight k subscript 1 plus 1 over straight k subscript 2 close parentheses
straight t subscript 1 superscript 2 space plus straight t subscript 2 superscript 2 space equals space fraction numerator 4 straight pi squared straight m space left parenthesis straight k subscript 1 plus straight k subscript 2 right parenthesis over denominator straight k subscript 1 straight k subscript 2 end fraction
straight t subscript 1 superscript 2 space plus straight t subscript 2 superscript 2 space equals space straight T squared