Answer
a) $1.98\times10^{20}N$
b) The magnitude of the gravitational force that the moon exerts on the earth is the same as that exerted by earth on moon.
Work Step by Step
a) The distance between earth and moon = r = $3.845\times10^{8}m$
magnitude of gravitational force the earth exerts on the moon =
$F=\frac{GMeMm}{r^{2}}=\frac{6.674\times10^{-11}\times 5.974\times 10^{24}\times 7.35\times 10^{22}}{(3.845\times10^{8})^{2}}=1.98\times10^{20}N$
b) As per Newton's third law, the magnitude of gravitational force that the moon exerts on earth is the same as that exerted by earth on the moon.
