Question

The speed of light is 3.0x10^5 km/sec and it takes light 1.3 seconds for light to travel from the moon to earth froim this information what is the distance to the moon

Answer 1

The motion of the light is a uniform motion with constant speed $v=3 \cdot 10^5 km/s$, therefore we can use the basic relationship between speed, space and time:
$v= \frac{S}{t}$ (1)
where S is the distance covered and t is the time taken. The light takes t=1.3 s to travel from the moon to Earth, therefore by rearranging eq.(1) we can find the distance between the Moon and the Earth:
$S=vt=(3 \cdot 10^5 km/s)(1.3 s)=390000 km=3.9 \cdot 10^5 km$