Question

Suppose planet earth suddenly grew in size, so that its radius was twice as large as before. Also suppose that at the same time, its mass also doubled to twice its former mass. If you weight used to be 700 N, what is it on this "new" Earth. Describe why this is the answer using appropriate formulas.

Answer 1

F = G m M/r^2
F' = G m 2M/(2r)^2

F'/F = 2/4 =1/2

700* 1/2 = 350 N

Answer 2

force= M/d^2

M is doubled, d is x2, so you have
a factor 2/4 or weight is 1/2 , or 350N