Question

Light in a vacuum travels at a constant speed of 3x10^8 m/s. If the moons average distance from the earth is 38776106 km how long would it take for a beam of light to travel from earth to the moon and back to earth again?

Answer 1

Answer: 258.3 s

Explanation:

The speed $s$ is given by the following equation:

$s=\frac{D}{t}$

Where:

$s=3(10)^{8} m/s$ is the speed of light in vacuum

$D=2(38776106 km \frac{1000 m}{1 km})=7.75(10)^{10} m$ is the double of the distance between Earth and Moon, since the beam of light travels from Earth to the Moon and back to Earth again.

$t$ is the time it takes to the beam of light to travel the mentioned distance

Isolating $t$ and solving with the given information:

$t=\frac{D}{s}$

$t=\frac{7.75(10)^{10} m}{3(10)^{8} m/s}$

Finally:

$t=258.3 s \approx 258 s$