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Unformatted text preview: m = 2.75 × 10 5 µg
EXAMPLE 1.12 The Factor-Label Method
The Voyager 2 mission to the outer planets of the solar system transmitted spectacular photographs of Neptune
to Earth by radio signals. Radio waves, like light waves, travel at a speed of 3.00 × 10 8 m/s. If Neptune was
2.75 billion miles from Earth during these transmissions, how many hours were required for radio signals to
travel from Neptune to Earth?
•Method of Solution
First state the problem.
? h = 2.75 × 10 9 mi
The speed of light can be written as a conversion factor because 1 s of time is equivalent to 3.00 × 10 8 m of
3.0 × 1 0 8 m
3.00 × 1 0 8 m
This will convert units of distance into units of time in seconds, but first the distance must be expressed in
meters rather than miles. To convert from the U.S. system to the SI, we can use 1.61 km = 1.0 mile. In
general, our plan will be:
distance → or t ime miles → k m → m → s → min → h
Notice that the time in seconds must be converted...
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- Spring '08