Homework 2
Due: Thursday, 11th April
Chapter 2
Show your work when required!
I promise this is one of the most mathematically challenging HW sets. Look at
your notes, the questions are similar to the examples done in
class. Give the questions a go!
a) Mercury orbits with a semi-major axis of 0.4 AU. What is the period of Mercury? (1 mark)
b) What is the period of a planet orbiting at 1 AU from a 9 Solar Mass star? (1 mark)
c) You observe a solar system with a planet that is 1 AU from the star. The orbital period of the planet is 9 years. What is the star's mass? (1 mark)
2.) Newton's Laws: A friend has a mass of 100kg. a) They step on weighing scales on Earth. How much do they weigh in Newtons? (1 mark)
b) The friend then goes to Planet X. Planet X has a mass twice that of the Earth and has a radius 1/2 that of the Earth. By what factor is the acceleration due to gravity larger on Planet X than on the Earth? (2 marks)
c) How much does the friend weigh on Planet X? (1 mark)
d) What is the friends mass on Planet X? (1 mark)
3) You discover a planet orbiting a star with the same mass as the sun. It's distance of closest approach is 3 AU, the furthest it gets from the star is 5AU.
a) Make a sketch of the system. Mark on the aphelion and perihelion positions and the position of the star.
(3 marks)
b) What is the semi-major axis? (1 mark)
c) What is the period of the planet's orbit? (1 mark)
4) Which planet rotates around it's sun fastest (with the shortest period): Planet A which rotates round a planet with mass 10 M_sun at a distance of 2 AU's or Satellite B that rotates around the planet with mass 5 M_sun that rotates around the planet at a distance of 1AU? Use proportionality to get full credit as shown in class. (4 marks)
5) Place these astronomers in chronological order (earliest first). Briefly (two sentences per person/bullett points is enough) describe their contribution to astronomy or what they thought the Universe was like. Copernicus, Brahe, Galileo, Newton, Kepler, Ptolemy. (6 marks)
Total 23 marks