# Physics Help : gravitational field

1. Oct 27, 2004

### alamin

Two stars, masses 10^20kg and 2* 10^20kg respectively, rotate about their common centre of mass with an angular speed of w. Assuming that the only force on a star is the mutual gravitational force between then, calculate w.
Distance = 10^6km and that G= 6.7*10^-11Nm^2/kg^2

2. Oct 27, 2004

### spacetime

Find out the location of center of mass. Let it be $$r$$ away from one of the stars.

Then use
$$\frac{G \mu m}{r^2} = mr \omega^2$$

where r is the reduced mass of the two stars.

$$\mu=\frac{Mm}{M+m}$$

spacetime
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