Rotational Motion Question 2

Question: Initial angular velocity of a circular disc of mass M is C ω1 . Then, two small spheres of mass m are attached gently to two diametrically opposite points on the edge of the disc. What is the final angular velocity of the disc?

[AIEEE 2002]

Options:

A) (M+mM)ω1

B) (M+mm)ω1

C) (MM+4m)ω1

D) (MM+2m)ω1

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Answer:

Correct Answer: C

Solution:

  • [c] Conservation of angular momentum gives 12MR2ω1=(12MR2+2MR2)ω2 (l1ω1=l2ω2 and l1=12mR2 s l2=12mR2+2mR2)

12MR2ω1=12R2(M+4m)ω2

ω2=(MM+4m)ω1



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