SOLUTION: Isubmitted this one before and the person and I had two totally different answers. I asked the teacher and he gave me some choices to choose from. The diameter of the Milky Way di

Question 84488: Isubmitted this one before and the person and I had two totally different answers. I asked the teacher and he gave me some choices to choose from.
The diameter of the Milky Way disc is approximately 9 * 10^20 meters. How long does it take light, traveling at 10^16 m/year to travel across the diameter of the Milky Way?
The choices are 900,000 years, 90,000 years, 9,000 years and 900 years. Ihave to say that I was not evenclose soI am definitely doing something way wrong.Please help?
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Since we're given a distance (the diameter of the galaxy) and a rate (the speed of light) and we want to find a time, we can use the distance-rate-time formula

where the distance (d) equals the rate (r) (or speed) multiplied by the time (t)

So let and and lets solve for t

Plug in and

Divide both sides by to solve for t

Now in order to reduce the left side , we can subtract the exponents.

Subtract the exponents using the identity

So it takes light 90,000 years to travel the diameter of the Milky Way.
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