 Solution

ID: past-exam-of-the-physics-1-paper-of-the-university-of-oxford/2017-resit/2/b/solution

A radial outward kick has no angular impulse about the centre. Therefore

Δ L = 0, Δ E = \frac{1}{2} m δ^{2} > 0.

The initial position is on the outward-moving portion of a bound elliptic Kepler orbit, between pericentre and apocentre, rather than at either turning point. The eccentricity is

e = δ / v_{c}

and the semilatus rectum remains

r_{0}

. The orbital energy change is second order: it vanishes to first order in the impulse but is positive for any nonzero kick.

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