Motion of Centre of Mass — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Motion of Centre of Mass.

CM motion in 2D/3D with varying external forces

medium

While basic CM velocity/acceleration calculations are common, NEET might introduce scenarios where external forces are not just gravity but also other constant forces, requiring vector addition of accelerations and potentially projectile motion analysis for the CM. This would test a deeper understanding of $\vec{F}_{ext} = M \vec{A}_{CM}$ in multiple dimensions, moving beyond simple 1D cases or zero external force scenarios. Students would need to resolve forces and accelerations into components.

System with changing mass (e.g., rocket propulsion simplified)

low

While the full rocket equation derivation is typically beyond NEET, conceptual questions about how the CM of a variable mass system behaves under external forces (or lack thereof) could appear. For instance, a system losing mass in one direction and gaining momentum in another. This would test the understanding of momentum conservation in a slightly more complex context than a fixed-mass system, focusing on the system's overall momentum rather than just individual particles.

Combined problems: CM motion with rotational dynamics

medium

NEET often integrates concepts. A problem could involve a rigid body (where CM motion is translational) also undergoing rotation. While the CM's translational motion is governed by external forces, the rotational motion is governed by external torques. A question might ask about the CM's path while the body is simultaneously rotating, requiring students to distinguish between translational and rotational aspects of motion. For example, a rolling object on an inclined plane, where the CM accelerates down the plane.

Conceptual questions on internal vs. external forces and CM trajectory

high

This is a perennial favorite. Questions testing the understanding that internal forces (like explosions, spring forces within a system, or forces in an inelastic collision) do not alter the trajectory of the center of mass are very common. Students need to correctly identify external forces (gravity, air resistance, friction) as the sole determinants of CM motion. These questions are often qualitative but require a solid conceptual grasp.