Read before you solve · 3 min
Read Impulses: Translation and Rotation Start Together
A horizontal impulse changes centre-of-mass momentum by p, while an off-centre hit also gives angular impulse p times h about the centre.
NSEP · Rotational Motion · 1 linked question · 100% coverage
Know this first
Motion and force questions become simpler when direction, starting condition, time and the acting forces are marked first.
Distance · Length of the path travelledDisplacement · Straight-line change in positionResultant force · Net force including direction
Study deeper: NCERT Physics · Rotational Motion
Start with the condition
v = p/M and I ω = p α R with I = 2MR squared/5
The immediate rolling condition
v = ω R, which selects the required impact height
Build the governing relation
Separate translational kinetic energy p²/(2M) from rotational kinetic energy L²/(2I); both were supplied by the impulse.
Finish with a physical check
Check the limiting case before selecting an option: remove the special feature in the diagram or make the relevant parameter very large or very small. The result should reduce to a familiar relation.
OlympIQ exam lens
- ✓State the physical condition before choosing a formula.
- ✓Keep direction, sign and constraint information explicit.
- ✓Test one limiting case before committing to an option.
OlympIQ trap
A central hit has zero torque and therefore no rotation—it is not pure rotational motion.
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