UPSEE 2018 Solved Paper

Two planets (each having mass m ) revolve around a stationary star (of mass M ) in a circle of radius r. The two planets are always on opposite side of the star (i.e. they are diametrically opposite and always having separation 2r ). The orbital period T of the planets is of the form T=2π√

r3

GM′

. What is the value of M′ ?