The planet Neptune is, on average, about 4.5 billion km from the sun. How long does it take light from the sun to reach Neptune? (Recall that the speed of light is about 300,000 km/s)
A)about 4 days
B)about 4 minutes
C)about 4 seconds
D)about 4 hours

Question

Quizplus · Accepted Answer

To calculate the time it takes for light to reach Neptune, we divide the distance between Neptune and the sun (4.5 billion km) by the speed of light (300,000 km/s). 
Time = Distance ÷ Speed 
Time = 4.5 × 10^9 km ÷ 3 × 10^5 km/s 
Time = 15,000 seconds 
This is equivalent to about 4.17 hours, so the best choice is D) about 4 hours.

The Planet Neptune Is, on Average, About 4