1. The problem statement, all variables and given/known data Spheres of masses m1 2.53kg and m27.16kg are fixed at a distance 1.56m apart centre to centre.A m3 212 g sphere is positioned 42cm from the 7.16 kg fromcentre of 7.16 kg sphere along the line of centres.How much work must be done by ext agent to move thesphere of 212 g sphere along the line of centres and place it 42 cm from the centre of sphere of mass 2.53 kg sphere?Assume the 212 g sphere to be moved bw the two spheres. 2. Relevant equations Wext(External)=-Wg(gravitational) 3. The attempt at a solution Wext=Gm3m2(1/.42-1/1.14)-Gm3m1(1/1.14-1/.42) Which is not giving the desired result of 98.5pJ. But if I take Wext=Gm3m2(1/.42-1/1.14)+Gm3m1(1/1.14-1/.42) the answer gets right.But why should it be a positive sign?