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A system of two identical spheres, each of mass 1.5 kg and radius 50 cm, is fixed at the ends of a light rod so that the separation between the centres is 5 m. The moment of inertia of the system about an axis perpendicular to the rod and passing through its midpoint is

Asked in JEE Main 31st Aug 2nd Shift 2021 · Standard bodies and axis theorems

• (1) 1.905×10⁵ kg m²
• (2) 18.75 kg m²
• (3) 19.05 kg m²
• (4) 1.875×10⁵ kg m²

Step-by-step solution

Why the other options are wrong

• (1) Comes from a stray factor of 10⁴ in the arithmetic.
• (2) Comes from treating the spheres as point masses and dropping the 2/5 mR² self term.
• (4) Comes from the same point-mass slip together with a power-of-ten error.

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