Question

On the planet whose size is the same and mass four times, as that of earth, find the amount of work (in $J$) done to lift $3\text{kg}$ mass vertically upwards through $3\text{m}$ distance on the planet. (The value of $g$ on the surface of earth is $10{\text{ms}}^{-2}$)

Answer 1

Total work done
$W_p=m\times g_p\times h$
where, $g_p=\frac{G{M}^{\prime }}{R^2}$ ....(1)
here given, $M^{\prime }=4M$
so, $g_p=\frac{4GM}{R^2}$
$g_p=4g\Rightarrow 4\times 10=40m/s^2$

Then, total work done =
$W_p=40\times 3\times 3W_p=360J$