9th Edition Textbook:
45) Distances by Light. Just as a light-year is the distance that light can travel in 1
year, we define a light-second as the distance that light can travel in 1 second, a
light-minute as the distance that light can travel in 1 minute, and so on. Calculate the
distance in both kilometers and miles represented by each of the following:
a. 1 light-second.
1 light second = 300,000 km
300,000km = 180,000 miles
b. 1 light-minute.
1 light second (60) = 300,000km (60) = 18,000,000km
180,000 miles (60) = 10,800,000 miles
c. 1 light-hour.
1 light second (60)(60) = 300,000km (3600) = 1.08 *10^9km
180,000 miles (3600) = 648,000,000 miles
d. 1 light-day.
300,000km(60)(60)(24) = 2.592 * 10^10 km
180,000 miles (60)(60)(24) = 1.5552 *10^10 miles
46) Spacecraft Communication. We use radio waves, which travel at the speed of
light, to communicate with robotic spacecraft. How long does it take a message to travel
from Earth to a spacecraft at
a. Mars at its closest to Earth (about 56 million km)?
56,000,000 km/ 300,000 km/s = 186.67 seconds * 1 min/60 seconds = 3.11 min
b. Mars at its farthest from Earth (about 400 million km)?
400,000,000 km/ 300,000 km/s = 1333.33 seconds * 1 min/60 seconds = 22.22 min
c. Pluto at its average distance from Earth (about 5.9 billion km)?
5,900,000,000 km / 300,000 km/s = 19666.67 seconds *1 min/60 seconds = 327.78 min
