2022 EOY ACSI P1 Q7

The planet Neptune is approximately \(4.5 \times 10^9\) km from the Sun. Given that light travels at \(3 \times 10^8\) km per second through interstellar space, find the time taken in seconds for light to travel this distance.[3]

Unit note: the supplied speed is written in km/s. Using that stated value gives 15 seconds. The usual approximation for light is \(3\times10^8\) m/s; with that unit, the same distance gives \(15000\) seconds. The recovered school worked-paper copy also prints km/s and gives 15 seconds; this is a source-level physical unit error.