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Question: Answered & Verified by Expert
A uniformly tapering conical wire is made from a material of Young's modulus Y and has a normal, unextended length L. The radii, at the upper and lower ends of this conical wire, have values R and 3R, respectively. The upper end of the wire is fixed to a rigid support and a mass M is suspended from its lower end. The equilibrium extended length, of this wire, would equal:
PhysicsMechanical Properties of SolidsJEE MainJEE Main 2016 (09 Apr Online)
Options:
  • A L1+29MgπYR2
  • B L1+19MgπYR2
  • C L1+13MgπYR2
  • D L1+23MgπYR2
Solution:
2680 Upvotes Verified Answer
The correct answer is: L1+13MgπYR2
r=2RLx+R

For a small section

FA=Ydldx

0LdL=0LMgdxπ2RLx×R2Y



L=MgπY-12RxL+R0L×L2R

=MgL3πR2Y

L f =L+ΔL=L[ 1+ mg 3π R 2 Y ]

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