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A solid sphere of mass 500 g and radius 5 cm is rotated about one of its diameters with an angular speed of 10 rad s⁻¹. If the moment of inertia of the sphere about its tangent is x×10⁻² times its angular momentum about the diameter, then the value of x will be ______.

Asked in JEE Main 11th April 1st Shift 2023 · Angular momentum of a rigid body

Answer: 35

Step-by-step solution

Work in SI: M=0.5 kg and R=0.05 m, so R²=2.5×10⁻³ m².

Moment of inertia about a tangent, by the parallel-axis theorem: Iₜ=2/5MR²+MR²=7/5MR².

Iₜ=1.4×0.5×2.5×10⁻³=1.75×10⁻³ kg m².

Angular momentum about the diameter: L=2/5MR²ω=0.4×0.5×2.5×10⁻³×10=5×10⁻³ kg m² s⁻¹.

Ratio: (Iₜ)/L=(1.75×10⁻³)/(5×10⁻³)=0.35=35×10⁻².

x=35.

The two quantities have different dimensions, so this ratio is not a physical constant — the question is simply asking for the arithmetic.

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