Grantham PHY220 Week 1 Assignment Problem 1

One lightyear is defined to be the distance light can travel in one year. What is this distance in meters? How long does it take for light to get to the Moon?

Solution:

$1\:lightyear=9.461\times 10^{15}\:m$

The approximate distance from Earth to the moon is 384,400 kilometers. The time it takes for the light to reach the moon is

$t=\frac{384400\:km\:\left(\frac{1000\:m}{1.00\:km}\right)}{299\:792\:458\:\frac{m}{s}}=1.28\:s$