Question

Light travels at a constant speed of 3.0×108 m/s in a vacuum. (a) It takes light about 1.3 seconds to travel from the Earth to the Moon. Estimate the distance of the Moon from the Earth's surface, in meters. (b) The astronomical unit (abbreviated AU) is equal to the distance between the Earth and the Sun. One AU is about 1.5×1011 m. If the Sun suddenly ceased to emit light, how many minutes would elapse until the Earth went dark?

Answer 1

Answer: a)3,9 x 10^8 m

b) 500 s =  8,33 minutes

Explanation: We know that the average speed is distance/time

so to calculate  the distance Earth to Moon  we use the above relation

d Earth-Moon = Light speed* time

On the other hand, to calculate the time when Earth will be dark,

we calculate   the spend time for the last ray of light coming from the sun

so  t = AU /Light speed