Question

The mass of the earth is $6.00\times {10}^{24}kg$ and that of the moon is $7.40\times {10}^{22}kg$. The constant of gravitation $G=6.67\times {10}^{-11}N-m^2/k{g}^2$. The potential energy of the system is $-7.79\times {10}^{28}joule$. The mean distance between the earth and moon is

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

$U=-\frac{GMm}{r}$
$\Rightarrow 7.79\times {10}^{28}=\frac{6.67\times {10}^{-11}\times 7.4\times {10}^{22}\times 6\times {10}^{24}}{r}$
$\Rightarrow r=3.8\times {10}^{8}m$