Example (N09/I/16) Binary Stars 

Two stars of mass M and 2M, at a distance 3x apart, rotate in circles about their common centre of mass O. 
The gravitational force acting on the stars can be written as  k G M 2 x 2 . 
What is the value of k? 
A  0.22             B  0.50                C  0.67             D  2.0



Model:

https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejss_model_gravity02_1/gravity02_1_Simulation.xhtml