Q.A body weighs 5.6 kg wt on the surface of the Earth. How much will be its weight on a planet whose mass is 7 times the mass of the Earth and radius twice that of the Earth's radius?

[!TLDR] With $g_p/g_E=(M_p/M_E)/(R_p/R_E)^2=7/4=1.75$, the weight on the planet is $5.6\ti …

Weight on a planet is $w=mg_{planet}$, and mass m stays the same everywhere, so the ratio of weights on two worlds equals the ratio of their g values. Given the planet has mass $M_p=7M_E$ and radius $R_p=2R_E$: $$\dfrac{g_p}{g_E}=\dfrac{GM_p/R_p^2}{GM_E/R_E^2}=\dfrac{M_p}{M_E}\times\left(\dfrac{R_E}{R_p}\right)^2=7\times\left(\dfrac{1}{2}\right)^2=7\times\dfrac{1}{4}=\dfra …

Form the ratio $g_p/g_E$ from the given mass and radius multiples, then scale the Earth weight by that rati …

Forgetting to SQUARE the radius ratio (since $g\propto1/R^2$, not $1/R$), which would give an …