Electronics and Communication Engineering - Exam Questions Papers - Discussion

Using law of gravitations, the force between the two point masses is F =

M₁ = mass of moon = 6.7 x 10²² Kg

M₂ = mass of earth = 6 x 10²⁴ Kg

r = distance between masses = 380 mm

G = universal gravitational constant = 6.7 x 10^-11 Nm²/Kg²

Let Q₁ and Q₂ be the charge on moon and earth respectively. Now the gravitational force must be balanced by the force of repulsion

Q₁Q₂ = 4pε₀M₁M₂G

but Q₂ = 10Q₁

= 10 x 4pω₀M₁M₂G

∴ Q₂ = 173 x 10¹²

Q₁ = 17.3 x 10¹² C

Q₁ = 17.3 TC.