JEE MainPhysicsRotational MotionNumerical+4 / −1
A solid sphere with uniform density and radius is rotating initially with constant angular velocity about its diameter. After some time during the rotation its starts loosing mass at a uniform rate, with no change in its shape. The angular velocity of the sphere when its radius become is . The value of is .
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Correct answer: 32
- Moment of inertia of the sphere
For a solid sphere of mass and radius , about a diameter:
Initially,
with angular velocity .
- What remains constant?
The sphere loses mass uniformly and its shape remains spherical. Since the lost mass leaves symmetrically, there is no external torque on the sphere.
Hence, angular momentum is conserved:
- Relation between mass and radius
Uniform density is maintained, so
Thus mass is proportional to :
When radius becomes ,
- Final moment of inertia
At radius ,
Substitute :
So,
- Use conservation of angular momentum
Cancelling :
Thus,
- Comparison with stored answer
Derived answer:
Stored correct answer:
They match.
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