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NEET PHYSICSRotational motionMedium

Question

A solid sphere is rotating about a diameter at an angular velocity ω\omega. If it cools so that its radius reduces to 1n\frac{1}{n} of its original value, its angular velocity becomes:

A

ωn\frac{\omega}{n}

B

ωn2\frac{\omega}{n^2}

C

nωn\omega

D

n2ωn^2\omega

Step-by-Step Solution

Since no external torque acts on the solid sphere as it cools and shrinks, its angular momentum (LL) remains conserved. According to the law of conservation of angular momentum, L=Iω=constantL = I\omega = \text{constant} .

The initial moment of inertia of the solid sphere is I1=25MR2I_1 = \frac{2}{5}MR^2, and its initial angular velocity is ω1=ω\omega_1 = \omega.

When the radius reduces to R2=RnR_2 = \frac{R}{n}, the new moment of inertia becomes: I2=25M(Rn)2=1n2(25MR2)=I1n2I_2 = \frac{2}{5}M\left(\frac{R}{n}\right)^2 = \frac{1}{n^2}\left(\frac{2}{5}MR^2\right) = \frac{I_1}{n^2}

Applying the conservation of angular momentum: I1ω1=I2ω2I_1\omega_1 = I_2\omega_2 I1ω=(I1n2)ω2I_1\omega = \left(\frac{I_1}{n^2}\right)\omega_2 ω2=n2ω\omega_2 = n^2\omega

Thus, its new angular velocity becomes n2ωn^2\omega.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from Rotational motion. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSRotational motionsphererotatingdiameterangularvelocity

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