1. Find the electric charge required on the earth and moon to balance their gravitational attraction if the charge on the earth is 12.5 times that on the moon.
Mass of moon = 6.7 x 1022 Kg
Mass of earth = 6 x 1024 Kg
Distance between moon and earth = 380 Km
Universal gravitational constant = 6.7 x 10-11 Nm2/Kg2

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By: guest on 01 Jun 2017 10.26 pm

Using law of gravitations, the force between 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 km 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 = 4p ε0M1M2G but Q2 = 12.5Q1 = 12.5 x 4p ω0M1M2G ∴ Q2 = 6.11 x 1014 Q2 = 61.11 TC Q1 = 4.89 TC.