Question

What is the size of the gravitational force that Earth exerts on the Moon?

The mass of the Moon is `7.35*10^22kg`, while that of Earth is `5.98*10^24kg`. The average distance from the center of the Moon to the center of Earth is `384,400 km`.

Answer 1

We use Newton’s universal law of gravitation, `F = -G( m_1.m_2)/r^2` but be careful to convert the distance to base units (m)

Explanation:

`F = -6.67xx10^-11(7.35xx10^22xx5.98xx10^24)/(384xx10^6)^2`

I get `F = -1.99xx10^20` N

The minus sign in the answer is because force is a vector quantity, written as `vecF`, so the direction matters and it is in the opposite direction to the distance as measured outwards from the Earth.