Q. The mass of the earth is $6.00 \times 10^{22}$ kg. The constant of gravitation $g = 6.67 \times 10^{- 11}Nm^{2}kg^{- 2}$. The potential energy of the system is $- 7.73 \times 10^{28}$ J. The mean distance between earth and moon is
A) $3.80 \times 10^{8}m$
B) $3.37 \times 10^{6}m$
C) $7.60 \times 10^{4}m$
D) $1.90 \times 10^{2}m$
Explanation
(a) $U = \frac{- GMm}{r}$ or $r = \frac{- GMm}{U}$
$r = \frac{- 6.67 \times 10^{- 11} \times 6 \times 10^{24} \times 7.4 \times 10^{22}}{- 7.79 \times 10^{38}}$
$= 3.8 \times 10^{8}m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.