Help physic gravitational (exam tomorrow)?

A binary star system has two stars of equal mass mstar, separated by a distance r. A comet of mass mcomet is very far away essentially at rest. Slowly, gravity pulls the comet towards the stars along a trajectory that passes through the midpoint between the two stars

question 1:a) Draw a free body diagram for the comet when it passes through the midpoint and find the net force acting on the comet at that point.

Question 2: Find the potential energy of the comet at the midpoint between the stars

Question 2 Find the potential energy of the comet at the midpoint between the stars

Question 3: Find the velocity of the comet when it passes through the midpoint between the two star

Those were what I try:

question 1: I put two opposite arrow (Fg) and said that the total net force is zero

question 2: Ug=-4Gm(start)m(comet)/r

question 3: v= sqrt(Gm(star))*2

my exam is tmr and my professor have not post the answer! help please