Question

Two identical spheres of radius 30mm and mass 2kg on the surface of the earth are placed in contact. Find the gravitational attraction between them.

Answer 1

The  gravitational attraction between two spheres is given by the Newton's gravitational law:

$$F = G\dfrac{m_1m_2}{r^2}$$

where $m_1 = m_2 = 2kg$ are masses of two identical spheres, $r = 2\cdot 30mm = 0.06m$ is the distance between their centers and $G = 6.67\times10^{-11} m^3kg^{-1}s^{-2}$ is the gravitational constant. Thus, obtain:

$$F = G\dfrac{m_1m_2}{r^2} = 6.67\times10^{-11} \cdot \dfrac{2\cdot 2}{0.06^2} \approx 7.41\times 10^{-8}N$$

Answer. $7.41\times 10^{-8}N$.