Energy & Matter

Fall 2009

• Start reading chapter 9 by Thursday, October 22. The most important section is pp. 161-165. Chapters 9 and 10 go together, so also read chapter 10 at this time. Pages 184-195 are the most important.

Assignment for chapter 8: Rotational Motion. Due Thursday, Oct. 29.

1. What is meant by tangential speed?

2. A 30N force is applied to the end of a wrench handle that is 0.25m long. What is the torque? 3. When a system is in equilibrium, how do the clockwise and counterclockwise torques compare?
4. What is the MASS of the box on the right if the system is in equilibrium, i.e. balanced? (You can assume the plank is supported at its center of gravity.)

5. What is the relationship between center of gravity and support base for an object in stable equilibrium?

6. If a skater who is spinning with arms extended pulls her arms in so that her rotational inertia is halved,

a) how much will her angular momentum change?

b) how much will her rate of spin (rotation speed) change?

Assignment for chapters 9 & 10: Due Thursday, October 29.. (staple this to the assignment for chapter 8.)

1. What is the magnitude of the gravitational force between the earth and a 6kg mass?

2. How does the force of gravity between two masses change if the distance between them is halved?

3. How does the force of gravity between two masses change if both masses are tripled?

4. Astronauts in orbit 300km above the surface of the earth appear to be weightless. Explain why. Is it because the force of earth’s gravity is so much less than it is on the surface of the earth?

5. Since the moon is attracted to the earth by the earth’s gravitational force, why doesn’t the moon crash into the earth?

• Read chapter 11 on the atomic nature of matter by Thursday, Oct. 27.