If the mass of moon is `(M)/(81)`, where M is the mass of earth, find the distance of the point where gravitational field due to earth and moon cancel each other, from the centre of moon. Given the distance between centres of earth and moon is 60 R where R is the radius of earth

Options

A. 4 R
B. 8 R
C. 12 R
D. 6 R

Answer

D

Explanation

Equating gravitational field intensities,
`((GM)/(81))/(r^(2))=(GM)/((60 R-r)^(2))`
Solving, we get `60 R - r = 9r :. r = 6 R`