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Question: Answered & Verified by Expert
A pendulum made of a uniform wire of cross sectional area A has time period T. When an additional mass M is added to its bob, the time period changes to TM . If the Young's modulus of the material of the wire is Y, then 1Y is equal to:
(g=gravitational acceleration)
PhysicsMechanical Properties of SolidsJEE Main
Options:
  • A 1-TTM2AMg 
  • B T M T 2 - 1 A Mg
  • C T M T 2 - 1 Mg A
  • D 1-TMT2AMg
Solution:
2134 Upvotes Verified Answer
The correct answer is: T M T 2 - 1 A Mg

Initial length =l. Time period T=2πlg        ...(i). After suspending mass M,. Youngs modulus Y=StressStrain=FAll=Fll A

Change in length of wire Δl=FlAY

Now time period TM=2πl+Δlg  ...(ii)       

TTM=2πlg2πl+Δlg        i ii

T2TM2=ll+Δl

Tm2T2=1+ll
1+FAY=TmT2putting value of l
1Y=TmT2-1AF
F=Mg
1Y=TmT2-1AMg

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