Determine to three significant figures the gravitational force acting between two spheres that are touching each other. The mass of each sphere is 900kg and the radius is 200mm.

The gravitational force acting between two objects is calculated by,

F = G x (m1 x m2) / d²

where G is the universal gravitational constant, m1 and m2 are the masses of the objects, and d is the distance between them. The distance between the spheres is twice the measure of the radius.

Substituting,

F = (6.674 x 10^-11) x (900 kg x 900 kg) / (0.40 m) ²

Thus, the gravitational force between the spheres is approximately 3.378x10^-4 N.