Physics 1135 Astronomy

Practice Problems for Exam 2

Vocabulary

• absolute magnitude
• absorption spectrum
• acceleration
• antimatter
• apparent magnitude
• blackbody radiation curve
• blue shift
• continuous spectrum
• deuteron
• doppler effect
• emission spectrum
• force
• frequency
• gamma rays
• infrared waves
• inverse square law of light, gravity, and electric charges
• joule
• light year
• luminosity
• neutrino
• Newton's three laws of motion and Newton's law of gravity
• parallax
• parsec
• positron
• radio waves
• red shift
• second of arc
• ultraviolet waves
• visible light
• watt
• wavelength
• x rays

Questions

1. You have travelled to the planet Tatooine, and one day observe the sun is directly overhead at your location. You are in radio contact with a colleague who is 1250 kilometers due north, who reports that the sun is 4 degrees away from the zenith at that location. Determine the circumference of Tatooine.
   
2. The planet Dagobah has a radius of 5000 km. If you observe its moon from two points on the planet that are separated by 5000km, you will observe a parallax angle of 0.6 degrees. What is the distance to the moon in kilometers?
3. The moon of the planet Dagobah (see previous problem) has an angular diameter of 0.25 degrees. What is the diameter of the moon in kilometers?
4. The mass of Dagobah is 4 * 10^{24} kg. Its radius is 5,000 km (=5,000,000 meters).
   (a) Calculate the acceleration of gravity at the surface of the planet.
   (b) Calculate how far an object will fall in 3 seconds on this planet, if air resistance is neglected.
   (c) Calculate the escape velocity at the surface of the planet.
5. What is the peak wavelength in the blackbody radiation for these objects: (a) a block of ice (T=273K); (b) a person with body temperature 310 K; (c) a metal pan heated to the boiling point of water (T=373K); (d) a metal object heated to 5000 K. Also calculate the frequency that corresponds to each of these wavelengths. Note: the wavelength answers you calculate will be in nanometers. To find the frequencies, it helps to know the speed of light (c) measured in nanometers per second:
   c=3 * 10^8 meters per second} times 10^9 nanometers per meter
   =3 *10^17 nanometers per second
6. If you know the frequency of a photon, what is the formula that tells its energy?
7. If a matter/antimatter collision results in 10 kilograms of matter being converted into energy, what is the total amount of energy that will be produced (in joules)? Use Einstein's formula, with this value for c:
   c=3 * 10^8 meters per second
8. Be able to explain in words how we determined the following:
   • the distance to the moon
   • the size of the moon
   • the mass of the Earth
   • the mass of the sun
   • the speed of light
   • the luminosity of the sun