No light does not need medium to travel.Its an electromagnetic(EM) wave.All EM waves travel independent of medium. In contrast mechanical waves need a medium,sound waves,shock waves are mechanical and they need medium to transfer energy or travel.
The mass affects the kinetic energy because the more the mass the more energy is given to the object and the speed<span> affects by making it go faster and longer, so whenever speed goes up so does energy.</span>
Explanation:
average speed = total distance travelled / total time travelled
time to travel the first 6km: 6 / 50 = 3/25 (h)
time to travel the next 6km: 6 / 90 = 1/15 (h)
[I think there's problem in the question 'cause 900km/h sounds impossible for normal person to travel in normal condition]
The total time: 3/25 + 1/15 = 14/75 (h)
Average speed over the 12 km drive will be:

I believe the correct answer from the choices listed above is option B. In a food chain. it is the producers trophic level that contains <span>the greatest amount of energy since it is the very start of the chain. Most of the energy are being stored and passed to the next organism. Hope this answers the question.</span>