Question

Using the formula for gravity, find the force of gravity on a 0.70-kg mass at Earth's surface. (The mass of Earth is 6×1024kg, and its radius is 6.4×106m.).

Answer 1

The Newton's law of universal gravitation states

$$F=G\frac{mM}{r^2}$$

So

$$F=6.67\times 10^{-11}\:\rm N\cdot m^2/kg^2\times \frac{0.70\:\rm kg\times 6\times 10^{24}\: kg}{(6.4\:\times10^6 \:\rm{m})^2}$$

$$=6.84\:\rm N$$