Physics 1090: Fundamentals of the Physical Universe

University of Wyoming

Unit 3: Momentum and Energy
Due September 16, 2009
10 points

To receive credit, your completed assignment must be submitted to me by the beginning of class on Wednesday, September 16.

Note that this homework is worth only 10 points instead of the usual 20. This is because the in-class presentations accounted for a large portion of this unit’s score.

Do one, and only one, of the following:

1. Reflect on the experience.

If you answered the reflection question last week, please answer a different question this week.

The activities for this unit consisted of a group investigation of one specific question. What were you feeling during the activity? Frustrated? Bored? Excited? Describe your feelings and try to determine the reasons for them.

2. Recount the process.

Tell the story of how your group looked for and found the relationship called for in the instructions. Who did what? What observations did you make? What experiments did you conduct? What ideas did you have, and how did you test them? Did you get stuck, and if so, how did you get yourselves unstuck? How did you settle on your answer?

3. Momentum.

What does it mean to say that “momentum is conserved”? How is momentum conserved in each of the following situations?

• When a moving car brakes to a stop.
• When two billiard balls collide.
• When a swimmer jumps off a raft.
 
4. Energy.

What is energy? Don’t just give a one-sentence definition; explain what it means. If you quote a dictionary or web definition, explain it in more detail with examples. This is a simple question, but the answer is not simple.

5. Educated mule.

This is a classic question to confront misconceptions about Newton's third law.

You hitch a wagon to your mule and direct him to pull. To your surprise, the mule instead tells you that he has studied physics, so he knows that no matter how hard he pulls on the cart, the cart will pull back just as hard on him. So, he continues, there is no point in even attempting to pull the cart, because it won't go anywhere.

Since you are studying physics, you know that Newton’s third law is true. So what is wrong with your mule's reasoning? Explain it clearly enough for your (English-speaking) mule to understand.

6. Secondhand knowledge.

Explain the “lesson” of ANOTHER group’s investigation. Summarize what they did, identify how it fits in this unit, and explain how their results illustrate, verify, or demonstrate a principle of physics.

Take your choice of these tasks. Do not submit answers to more than one of them. Just choose one, and submit it. Your answer should thoroughly address all points of the question. An adequate answer will be several paragraphs long.

Warning: Do not turn in paper that has ragged edges! If you write your work in a spiral-bound notebook, trim the edge before submitting it. Papers with ragged edges will be returned unmarked.