Given, distance between centre of ring and sphere, d=8​R Since, gravitational field at the axis of ring, E=(d2+R2)3/2Gmd​ Here, G is the gravitational constant. ⇒E=(8R2+R2)3/2GmR8​​=(3R)3GmR8​​⇒E=27R3GmR8​​=27R2Gm8​​ Force between ring and sphere, F=ME . . . (i) Substituting the value of E in Eq. (i), we get F=278​​R2GmM​