- #1

Zynoakib

- 70

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## Homework Statement

Plaskett’s binary system consists of two stars that revolve

in a circular orbit about a center of mass midway between

them. This statement implies that the masses of the two

stars are equal. Assume the orbital speed

of each star is 220 km/s and the orbital period

of each is 14.4 days. Find the mass M of each star.

## Homework Equations

## The Attempt at a Solution

Kelper's 3rd Law

Mass of the planet = (4(pi)^2(r)^3)/GT^2

T = 1244160

r = 8.72 x 10^10

G = 6.672 x 10^-11

Mass = 2.54 x 10^32, but the answer is 1.26 x 10^32 which is exactly half of my answer

why should I further divide my answer by 2? Is it because there are two planets in the system? But if I use the same equation to calculate the Sun's mass, I just need to substitute all those unknown into the equation without the need to consider the mass of the Earth. So what's wrong?

Thanks in advance!