Motion of System of Particles and Rigid Body — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Motion of System of Particles and Rigid Body.

Comparative Rolling Motion on Inclined Plane

high

NEET frequently asks to compare the acceleration or time taken for different rigid bodies (e.g., solid sphere, hollow sphere, disc, ring) to roll down an inclined plane. This tests the understanding of how moment of inertia ($I_{CM}/MR^2$ factor) affects acceleration. Questions might involve ranking bodies or calculating the ratio of accelerations/times. Students need to memorize or quickly derive the $I_{CM}$ for standard shapes and apply the rolling acceleration formula $a = rac{gsin heta}{1 + k^2/R^2}$.

Conservation of Angular Momentum with Variable Moment of Inertia

high

Problems where the moment of inertia of a system changes, leading to a change in angular velocity, are very common. Examples include an ice skater, a person walking on a rotating platform, or a mass dropped onto a rotating disc. These questions directly test the principle $I_1omega_1 = I_2omega_2$. The challenge often lies in correctly calculating the initial and final moments of inertia for the system.

Combined Translational and Rotational Kinetic Energy

medium

Questions might involve calculating the total kinetic energy of a rolling body or using energy conservation principles for rolling motion (e.g., finding the velocity at the bottom of an incline). This requires correctly summing $K_{trans} = rac{1}{2}Mv_{CM}^2$ and $K_{rot} = rac{1}{2}I_{CM}omega^2$, often using the $v_{CM} = Romega$ condition. Understanding the distribution of energy between translational and rotational forms is key.

Center of Mass of Composite Bodies or Systems with Missing Parts

medium

While basic CM calculations are common, NEET might pose slightly more complex problems involving finding the CM of a composite body (e.g., a disc with a smaller disc removed) or a system of particles where one particle's position needs to be determined for the CM to be at a specific point. This tests the algebraic manipulation of the CM formula and conceptual understanding of weighted averages.