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NEET PHYSICSRotational motionMedium

Question

A disc and a solid sphere of the same radius but different masses roll off on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first?

A

Disk

B

Sphere

C

Both reach at the same time

D

Depends on their masses

Step-by-Step Solution

The acceleration of a body rolling down an inclined plane without slipping is given by the formula a=gsinθ1+k2R2a = \frac{g \sin \theta}{1 + \frac{k^2}{R^2}}, where kk is the radius of gyration and RR is the radius of the body. For a solid sphere, the moment of inertia is I=25MR2I = \frac{2}{5}MR^2, so k2R2=25=0.4\frac{k^2}{R^2} = \frac{2}{5} = 0.4. For a uniform disc, the moment of inertia is I=12MR2I = \frac{1}{2}MR^2, so k2R2=12=0.5\frac{k^2}{R^2} = \frac{1}{2} = 0.5. Since k2R2\frac{k^2}{R^2} is smaller for the solid sphere, its acceleration aa will be greater than that of the disc (asphere>adisca_{\text{sphere}} > a_{\text{disc}}). The object with greater acceleration will take less time to cover the same distance and reach the bottom first. Also, the acceleration is independent of the mass of the rolling body. Therefore, the solid sphere will get to the bottom first.

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 motionsphereradiusdifferentmassesinclined

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