To be more specific on the problem, a 50kg astronaut, an 80kg astronaut and a 20kg rock are tied together by a light rope during a space walk. I am asked to find the center of mass.
Now, I've chosen my reference point as the 50kg astronaut and I've used the formula $(m_1r_1+m_2r_2+m_3r_3)/(m_1+m_2+m_3)$ to find the position of the center of mass ($r$) of the system. I am uncertain if this is the correct method used.
If someone could just inform me if i am on the right track. Thanks.