The distance between the centres of the Moon and the earth is D. The mass of the earth is 81 times the mass of the Moon. At what distance from the centre of the earth, the gravitational force will be zero?

Answer

2

Explanation

Let the given point be called P
If the magnetic field at P is zero, the direction of the current in the loops must be opposite
Using the formula for magnetic field at a point on the axis of a loop, `(mu_(0)I_(1)R^(2))/(2(R^(2)+(2R)^(2))^(3/2))=(mu_(0)I_(2)(4R)^(2))/(2((4R)^(2)+(2R)^(2))^(3//2))implies(I_(1))/(I_(2))=2`