The weight of a body on the earth is 98 N. If it is taken to another planet whose mass is double the mass of the earth and radius is double the radius of the earth, what is its weight?

: Weight of a body on the earth=98 N  

Let M be the mass of the earth and R is the radius of the earth
$$\begin{gathered} {\mathrm{M}}_{\mathrm{p}}=2\mathrm{M} {\mathrm{R}}_{\mathrm{p}}=2\mathrm{R} \\ \mathrm{Acceleration} \mathrm{due} \mathrm{to} \mathrm{on} \mathrm{the} \mathrm{plant} =\frac{{\mathrm{GM}}_{\mathrm{p}}}{{\mathrm{R}}_{\mathrm{p}}} \\ =\frac{\mathrm{G}2\mathrm{M}}{4{\mathrm{R}}^2} \\ =\frac{\mathrm{g}}{2} \\ \mathrm{Weight} \mathrm{on} \mathrm{the} \mathrm{planet} =\frac{98}{2} \\ =49\mathrm{N} \end{gathered}$$