Question

Calculate the force of gravity on the 0.60-kg mass if it were 1.3×107m above Earth's surface (that is, if it were three Earth radii from Earth's center).

Answer 1

The force of gravity between two objects is given by:
$F=G \frac{m_1 m_2}{r^2}$
where
G is the gravitational constant
m1 and m2 are the masses of the two objects
r is their separation

In this problem, the mass of the object is $m_1=0.60 kg$, while the Earth's mass is $m_2=5.97 \cdot 10^{24} kg$. Their separation is $r=1.3 \cdot 10^7 m$, therefore the gravitational force exerted on the object is
$F=(6.67 \cdot 10^{-11}m^3 kg^{-1} s^{-2}) \frac{(0.60 kg)(5.97 \cdot 10^{24} kg)}{(1.3 \cdot 10^7 m)^2}=1.4 N$