Question

Light from the Sun takes 8 minutes to reach Earth. How long does it take to reach Mars?

What is the Given & Unkown(s):
8 minutes (light to reach the sun)
t=?

Approprite formula:
?
Conversion of the formula in order to determine your unknown:
?

Inserting numbers:
8 min/ 1 Au = t/ 1.52 AU
t= (8 min x 1.52 AU)/ 1 AU = 12.2 min

Units:
?

(I don't know what to put for those 3 parts)

Answer 1

Based on speed of light (300,000 km/s): ca. 12 min. 40 sec.
Based on 8 min. from Sun to Earth: ca. 12 min

Explanation:

To compute the time, we need the following data:
Speed of light in vacuum: `c=300 000 (km)/s`
(More exactly 299 792 458 m/s, but for our purposes the round figure of 300 000 fits nicely)

Distance from Sun to Mars: 228 000 000 km.
(Distance from Sun to Earth: `150 000 000 km`, but we don't really need that figure.)
The only two items we need, are really the speed of light and the distance it has to travel, as our calculation then becomes:

time in seconds = Distance / speed of light

= `[228000000 km] / (300000 (km)/s)`

= `760 sec = 12 min 40 sec`

If we instead base our computation on the data we have been given, i.e. that the light uses 8 min. = 480 sek. to reach the earth, we must use the ration between Earth's distance and Mars' distance to the Sun, i.e.

`480 sec *(228 000 000 km)/(150 000 000 km)`

=`(480*228)/150 sec` = `730 sec ~~ 12 min`