 Solution

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

For a small opposing tangential kick,

Δ E = - m v_{c} δ + \frac{1}{2} m δ^{2} < 0, Δ L = - m r_{0} δ < 0.

The new tangential speed is less than the circular orbital speed, so the kick point is the apocentre of an ellipse. The orbit falls inward from the original circle. The signs assume

0 < δ ≪ v_{c}

; a large velocity reversal is outside the stated small-impulse regime.

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