These are all discussion questions:

1. Harold got a great deal on paper towels and so he has bought a very large boxful: 100 Kg!
A. When he exerts a constant force of 300 N, nothing happens. What is the friction force? (The answer is a number, which you need to explain).

B. He finds he can slide the box across the parking lot at 1 m/sec by applying a constant force of 500 N. What is the friction force now? (The answer is a number, which you need to explain).

C. What would happen if he applied a constant force of 600 N instead? (There is a numerical answer, which you need to explain).

2. Discussion question: Lay a piece of paper on the table, and then put a book on it. If you move the paper so that the acceleration is always small, the book will move with the paper and you can pull the book right off the table. If you try to accelerate the paper too much, it will slip out from under the book. Explain what is happening in each case, and explain what "small" and "too much" mean -- where is the dividing line between these two cases?

3. A game you can play is to give a penny a shove so that it slides across a table, trying to get it to stop on a target. Let's focus on what happens after the penny is launched: assume it is already moving at 1 m/sec. The sliding friction force is 0.002 N, and the mass of the penny is 0.004 Kg.
A) Describe the role that the friction force plays in this game.

B) Assume that the penny has just been launched with speed 1 m/sec. Explain how friction and the laws of motion determine how long the penny keeps moving.

C) Explain how the penny comes to a stop using the energy concept. How far does it go?

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