Karla Peck
Astronomy
Exercise I
Show your work!
1.
Write down the abbreviation for the following quantities, which are also nonSI units,
and then define them:
a. light year: ly,
The distance that light travels in a vacuum in 1 year.
b. parsec: pc, A unit of distance equal to 3.26 lightyears.
c. megaparsec: Mpc, One million parsecs.
d. arcsecond: arcsec, One sixtieth of a minute of arc.
e. Astronomical Unit :
AU, The average distance between the Earth and the Sun: 1.5 108
km = 93 million mi.
f. degree: A unit of angular measure or a temperature measure.
2. Express the following in scientific notation:
a. The distance to Sirius from Earth, 81,480,000,000,000,000 m
2.6 parsecs (8.6 lightyears)
b. The radius of a hydrogen atom, 0.00000000005392 m
10^10m
3.
A comet with a radius of 15 km has a mass of 10
11
kg and is traveling at 28 km/s
(relative to Earth).
What is the kinetic energy of the asteroid in Joules?
(Hint: First
convert 28 km/s to m/s then use the equation for kinetic energy on page 56.)
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4. If the asteroid in question 3 were to impact Earth at this speed, what would the energy
released be in tons of TNT?
If you did not get an answer to 3, assume the answer was
4.14 x 10
16
J. (1 ton of TNT = 4.184 x 10
9
J)
5.
What is the gravitational potential energy of a 400 kg satellite that is orbiting the earth
at 400 km above the surface of the earth? (Hint:
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 Spring '11
 WilsonKey
 Astronomy, Kinetic Energy, Astronomical unit, Lightyear, Karla Peck

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