Consider a planet in space whose mass is twice that of earth and radius is thrice that of earth what will be the weight of a body on this planet if its weight on the earth is 900N ??

Answer 1

(This must be math...)

F = G Mm/r^2
If M is doubled then F will be doubled.
If r is tripled then F is reduced to 1/9
The overall effect is 2 x 1/9 = 2 / 9
so W(on Earth) / w (on planet) = 2 / 9
W(on Earth) = 900 x 2 / 9 = 200 N