Question

If the speed of light is equal to $3\times {10}^{8}m{s}^{-1}$, how many kilometers will make up 1 light year?

• A. $946\times {10}^{13}$km
• B. $1.095\times {10}^{11}$km
• C. $1095$ km
• D. $9.46\times {10}^{12}$km

Answer 1

The correct option is D

$9.46\times {10}^{12}$km

One light year is the distance travelled by light in one earth year, that is in 12 months, or 365 days.
Therefore time taken $=365\times 24\times 60\times 60=31536\times {10}^{3}s$
Speed of light $=3\times {10}^{8}m{s}^{-1}$
1 light year = speed of light x time $=3\times {10}^8\times 31536\times {10}^3=9.46\times {10}^{15}m$ $=9.46\times {10}^{12}km$