 Solution

ID: past-exam-of-the-physics-b-course-of-the-university-of-cambridge/2021/paper-1/section-b/b6/a/solution

Kepler's first law: a bound planetary orbit is an ellipse with the central attracting body at one focus.
Kepler's second law: the line from that focus to the planet sweeps equal areas in equal times, equivalent to constant areal velocity.
Kepler's third law: the squared orbital period is proportional to the cube of the semi-major axis, $T^{2} = 4 π^{2} a^{3} / (GM)$ when the orbiting mass is negligible.

The first law includes a circular Kepler orbit as a special case. The third-law constant is the same for bodies orbiting the same dominant mass.

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