Question
a double star consist of 2 stars of mass m & .2m. distance b/w them is r. d 2 stars revolve under their mutual gravitatn force then d 2 stars have equal periods of revolution . HOW?
Joshi sir comment
according to newtons third law both star will give equal force to each other
so for first star of mass m, m(2r/3)ω2 = F or ω = [3F/2mr]1/2
similarly for second 2m(r/3)ω2 = F or ω = [3F/2mr]1/2
here 2r/3 and r/3 are taken according to centre of mass criteria.