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Question: Answered & Verified by Expert

AB is a light rigid rod, which is rotating about a vertical axis passing through end  A . A spring of force constant k and natural length l  is attached at A and its other end is attached to a small bead of mass  m. The bead can slide without friction on the rod. At the initial moment, the bead is at rest (w.r.t the rod) and the spring is unstretched. Select incorrect options :

PhysicsLaws of MotionJEE Main
Options:
  • A Vmax=mω2l2k-mω2
  • B Vmax=mω4l2k-mω2
  • C Vmax=mω4l2mω2-k
  • D Vmax=mω2l2mω2-k
Solution:
1041 Upvotes Verified Answer
The correct answer is: Vmax=mω4l2k-mω2
Velocity will be maximum at the equilibrium position

kx=mω2l+x

⇒   x=mω2lk-mω2

Now, using work-energy theorem
    

KE= Work done by all the forces

12mVmax2=0xmω2l+xdx-12kx2

⇒   Vmax2=2mω2lx+mω2x2-kx2m

Vmax2=mω2l+mω2l+x-kxxm

=mω2lxm

⇒   Vmax2=ω2lx=mω4l2k-mω2

Vmax=mω4l2k-mω2

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