## Statement

Knowing that the Moon takes 28 days to make one complete revolution around the Earth, calculate its average speed.

** Datum:** Consider the trajectory of the Moon as circular with a radius of 384,000 Km.

## Solution

First, we change the 28 days to seconds.

$$28\overline{)\text{days}}\times 24\overline{)\text{h}}\text{/}\overline{)\text{day}}\times 60\overline{)\text{min}}\text{/}\overline{)\text{h}}\times 60\text{s/}\overline{)\text{min}}=2419200\text{s}$$

Then we calculate the length of the circumference, which is the distance traveled by the Moon in its journey of 28 days. Considering R = 384,000 Km = 384,000,000 m:

$$L=2\xb7\mathrm{\pi}\xb7\mathrm{R}=2412743157.95696256\text{m}$$

Finally, we calculate the speed:

$${V}_{\mathrm{avg}}=\frac{\u2206s}{\u2206t}=\frac{2412743157.95696256}{2419200}=997.331\text{m/s}$$