Physics 9702/43 — May/June 2020

State what is meant by a gravitational force.

A binary star system consists of two stars $S_1$ and $S_2$, each in a circular orbit.

The orbit of each star in the system has a period of rotation $T$.

Observations of the binary star from Earth are represented in Fig. 1.1.

Observed from Earth, the angular separation of the centres of $S_1$ and $S_2$ is $1.2 \times 10^{-5}\ \text{rad}$.
The distance of the binary star system from Earth is $1.5 \times 10^{17}\ \text{m}$.

Show that the separation $d$ of the centres of $S_1$ and $S_2$ is $1.8 \times 10^{12}\ \text{m}$.

The stars $S_1$ and $S_2$ rotate with the same angular velocity $\omega$ about a point P, as illustrated in Fig. 1.2.

Point P is at a distance $x$ from the centre of star $S_1$.
The period of rotation of the stars is 44.2 years.