Rotational mechanics is one of the highest-yield chapters in JEE Physics — and one of the most mistake-prone. Here are the five errors we see most often.
Always apply the right-hand rule before writing any equation, not after. Guessing the sign and fixing it later is how sign errors slip into your final answer unnoticed.
If the rotation axis doesn't pass through the center of mass, you need:
I = I_cm + Md²
Students often use the standard moment-of-inertia formula for a different axis than the one specified in the question.
The condition v = ωR only holds when there's no slipping — it's a constraint, not a given fact. Always check whether the problem actually states this before using it.
Static friction in rolling motion can point either forward or backward depending on whether the object is accelerating or decelerating — don't assume it always opposes motion.
These are conserved under different conditions. A common trap: assuming angular momentum is conserved just because no external torque acts along one axis, while ignoring torques along others.
Master these five and you'll eliminate the majority of careless-mistake losses in this chapter.