# Unit 4: End of Unit Exam

This assignment consists of four parts. The first is a review with a couple of practice questions linked directly to their answers. The second is a short quiz that you take using Blackboard. It will be instantly scored for you by Blackboard; you only get one chance to take it, however, so be sure you are ready! The third part is an essay question. The question appears below; when you are ready to answer it, log on to Blackboard and submit your essay. Finally, for each unit, you should log on to Blackboard and contribute a question, an answer, or a comment to one of the posted topics. If you would like to introduce a new topic instead of contributing to an existing thread, please send your topic idea to your instructor. If you find the material in this unit challenging, you might want to start with the "discussion" part of the assignment in order to get some help with some of the ideas.

To use Blackboard you will need to be signed up as a student in the course. That means that first you must enroll for credit and then you can login to Blackboard. The instructor will verify that you are enrolled in the course and verify your enrollment in NorthStar.

Brief summary of Unit Four:

We started this unit by describing how familiar objects move near the Earth's surface under the influence of gravity when thrown. Then, we considered what their motion would look like if we threw them hard enough to go into orbit around the Earth. Finally, we ended with a discussion of several kinds of orbits around the Earth.

Before you go to the quiz, see how you do on these two questions. If you have trouble, you might want to review the unit, send a question to the discussion group, or seek help from the instructor.

Practice Question One

To maintain a constant distance from the surface of the Earth, a satellite must have a low ___________ orbit.

Practice Question Two

A satellite in a circular 24-hour orbit remains over the same spot on the Earth's surface. This means that it is motionless with respect to the Earth. Therefore, it should fall to Earth. Explain if this reasoning is correct or incorrect.

You will get instant feedback on your score on Quiz Four (and your instructor will also be informed of your score). If your score is OK, you may proceed directly to the Essay Question Four on Blackboard. Otherwise, you might want to look at what you missed, ask your instructor about questions you missed, or review relevant parts of the unit.

Essay Question

Unit 4. Match the descriptions of the orbit in words with the descriptions in numbers, and explain in each case what gave you the clue that told you how to match it:
a. The motion of a baseball when a home run has been hit.
b. The orbit of a satellite launched by the simple means of pushing it out of the bay of the Space Shuttle.
c. The motion of a spacecraft that is always located over the same part of the Earth.
d. The motion of a spacecraft on its way from Earth to Mars.
Orbit 1: Semi-major axis = 1.262 AU, perihelion 1AU.
Orbit 2: Semi-major axis 3189km, highly eccentric.
Orbit 3. Orbital period 90 minutes, semi-major axis about 6500 km.
Orbit 4. Semi-major axis 22,000 miles (35,000 km), eccentricity 0.

Don't forget to contribute to the discussion on Blackboard on one of the topics in this unit!