Before the Exam: 5 Things to Memorise

1. $K^{2}$/$R^{2}$ values in order: $\frac{2}{5} < \frac{1}{2} < \frac{2}{3} < 1$ (solid sphere → disc → hollow sphere → ring)

2. Disc about diameter: $I = MR^2/4$ (not $MR^2/2$). The $MR^2/2$ is for the central perpendicular axis.

3. Tangent formulas: Disc in-plane tangent = $5MR^2/4; sphere tangent = \7MR^2/5$.

4. Rolling speed formula: $v = \sqrt{2gh/(1+K^2/R^2)}$. For disc: $\sqrt{4gh/3}$. For ring: $\sqrt{gh}$. For solid sphere: $\sqrt{10gh/7}$.

5. KE ratio in angular momentum conservation: $KE_f/KE_i = I_i/I_f$ (when L is conserved).

In the Exam: Elimination Strategy

• If the question asks "which body reaches first?": always check $K^2/R^2$. Smallest wins.
• If options include $2MR^2/5$ for "tangent to sphere": eliminate it — that's just the diameter value (trap!).
• If asked about the perpendicular axis theorem for a cylinder or sphere: the answer is NO (invalid).
• For angular momentum conservation problems: check if the question asks for KE (not L). KE changes even when L is conserved.

Time Management for Rotational Motion Questions

• Standard I value: 30 seconds
• Axis theorem application: 45–60 seconds
• Rolling race ranking: 20 seconds (just check $K^2/R^2$)
• Conservation of L + KE ratio: 60–90 seconds
• Numerical rolling/incline problem: 90 seconds

Most Likely NEET Question This Year

Based on pattern analysis, the most probable question involves either:

• Finding I of a disc or sphere about a tangent (requiring both perpendicular and parallel axis theorems), or
• An ice skater/turntable problem where I changes and you must find $\omega_f$ and compare KE.

Practise these two types until they feel automatic.$