Read before you solve · 3 min

Read Rolling Points: Add Translation and Rotation as Vectors

This short read prepares one exact NSEP pattern: speed of points on a rolling disc. Identify the physical condition before calculating.

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 physical model

Read the configuration once, state the conserved quantity or governing law, and mark any changing geometry, sign convention or limiting condition.

For pure rolling,

\omega = v/R=4/0.10=40 rad s^{-}¹

Initially point B is halfway from the centre to the top, so its speed is the sum of translational speed v and rotational speed v/2, giving

vB = 6 m s^{-}¹

For point A on the rim after rotation angle φ, vA 2=2v2(1+cosφ).

Set vA = 6 m s⁻¹: 36=32(1+cosφ), so cosφ=1/8 and φ≈1.445 rad. t=φ/ω≈1.445/40=0.036 s

Check units, sign and one limiting case. A valid result must still fit the original geometry and stated constraint.

OlympIQ trap

Speeds on a rolling rim are not obtained by simply adding magnitudes except when the two velocities are collinear.

100% coverage across the linked question.