well, if your talking about circles, you could get the ball to point away from the circle, you can calculate the angle between the 2 objects with the atan2 method and set the xvel and yvel using trigonometry
Strictly speaking i dont think thats 100& perfect physics, but it looks close to the real thing, and in my opinion, why would you take a much longer path to the same results?
formulas:
angle:
xdif = obj2.x-obj1.x
ydif = obj2.y-obj1.y
angle = Math.atan2(ydif, xdif)
Trig:
xvel = Math.cos(angle*(Math.PI/180))
yvel = Math.sin(angle*(Math.Pi/180))