Question

Astrology, that unlikely and vague pseudoscience, makes much of the position of the planets at the moment of birth. The only known force a planet exerts on earth is gravitational.(a) Calculate the gravitational force exerted on a 5.00 kg baby by a 130 kg father 0.200 m away at birth (assisting so he is close).

Answer 1

The gravitational force is given by Newton's law of gravitation:

$\begin{gathered} F=G\frac{m_1m_2}{r^2} \\ \text{ where:} \\ G\text{ is the gravitational constant }6.67\times10^{-11} \\ m_1\text{ and }m_2\text{ are the masses of the objects } \\ r\text{ is the distance between the objects} \end{gathered}$

In this case the masses are 5 kg and 130 kg and the distance is 0.2 m; then we have:

$\begin{gathered} F=(6.67\times10^{-11})\frac{(5)(130)}{(0.2)^2} \\ F=1.084\times10^{-6} \end{gathered}$

Therefore, the force exerted is

$1.084\times10^{-6}\text{ N}$