Read before you solve · 3 min

Read Central Scattering: Keep Angular Momentum in the Energy

This short read prepares one exact NSEP pattern: elastic scattering in an inverse-cube force. Identify the physical condition before calculating.

NSEP · Mechanics · 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 · Mechanics

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 F(r)=K/r3 repulsive, choose U(∞)=0. Then U(r)=K/(2r2).

Angular momentum L = mv0b

At closest approach r, radial speed is zero, so (1/2)mv0 2 = L2/(2mr2) + K/(2r2).

Here m = 10-10 kg and v0=105 m s⁻¹, hence mv0 2=1 numerically

With K = b2, the equation gives r2=2b2, so r=b√2

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

OlympIQ trap

At closest approach radial velocity is zero, not total velocity; the angular-motion term remains.

100% coverage across the linked question.