Homework 03

Please answer at least 4 of the following 5 questions correctly for full credit:

Question 1

On an elliptical orbit: Where does a planet move fastest?

Question 2

Things moving in empty space (moon, stars, galaxies, satellites, ...) do not experience friction the same way things moving on Earth do. Why will they still not provide examples for the ideal undisturbed motion postulated in Newton's first law of motion, the law of intertia?

Question 3

If two ice-scaters push apart from each other, they excert forces on each other that are opposite in direction and equal in strength (Newton's third law). Let us assume they are initially at rest (and push in the same direction that the blades of their skates are oriented in...). After they are done pushing and let go of each other: Who will go faster: the lighter or the heavier of the two? Please tell us why.

Question 4

If you use the units pounds for mass, hours for time, and miles for distance: What units will the constant in Kepler's third law have? Please make sure you get the right powers of the basic units that are involved; one of the units I mention above should not be showing up in your answer.

Question 5 (the quantitative one...)

Gravitation is what keeps the planets on their orbits around the Sun, and satellites as well as the Moon on their orbits around the Earth. By what factor is the acceleration produced by the Earth's gravitational pull larger at geostationary satellite orbits than at the moon's orbit? Use 36 km for the radius of the geostationary orbit and 360,000 km for the radius of the Moon's orbit. (this is just a little bit less than the closest the Moon's elliptical orbit gets to earth. At the farthest the Moon is a little more than 400,000 km away from the earth.)
Correction: the geostationary orbit is at 36,000 km, not 36 km!!!

Please submit your answer as plain test in the main message body of an e-mail to kai-1060-hw@physics.utah.edu before midnight (MST) on January 31, 2008. Plain text in the main message body of your e-mail means no attachments!!!

Last modified: Fri Feb 1 10:34:29 MST 2008