Reading:

Cutnell and Johnson, Chapters 7.

Problems for Review:

Reviewing these problems gives you good exposure to this week's main topics, in practice. All solutions are posted on our website |http://www.cc.emory.edu/PHYSICS/Faculty/Benson/141/review.html|. Quantitative solutions are also in the Student Study Guide.

Conceptual:

MCAT review problem 8 (on website), from last time.

Quantitative:

Chapter 7, problems 31, 35, 39, 51, 53.

Problems to Hand In:

Conceptual:

Use the following to answer questions 1 -- 7:

A young girl decides to play on her sled, which is resting on a frozen and frictionless pond. The 20 kg girl slides across the ice at a speed of 2 m/s and collides with the 20 kg sled. Now stuck on the sled, she continues to slide until she and the sled hit a 50 kg log that is embedded in the ice.

1. What is the velocity of the center of mass of the child/sled system, after the (first) collision?
   1. 1 m/s
   2. 2 m/s
   3. 4 m/s
   4. 0 m/s
   
   
2. Which of the following would increase the child's velocity after the (first) collision?
   1. Increasing the child's initial velocity
   2. Increasing the child's mass
   3. Increasing the sled's mass
   4. Decreasing the child's mass
   
   
   1. i only
   2. i and ii only
   3. i and iii only
   4. iii and iv only
   
   
3. Which of the following statements are true about the child/sled system during the (first) collision?
   1. Kinetic energy is conserved; momentum is conserved.
   2. Kinetic energy is not conserved; momentum is conserved.
   3. Kinetic energy is not conserved; momentum is not conserved.
   4. Kinetic energy is conserved; momentum is not conserved.
   
   
4. The sled strikes the log and comes almost immediately to a full stop. Which one of the following statements is true about this process?
   1. The log applies a force to the sled; this force is larger than the force applied by the sled to the log.
   2. Momentum of the child/sled system is conserved; its kinetic energy is not conserved.
   3. Momentum of the child/sled system is not conserved; its kinetic energy is conserved.
   4. The sled applies a force to the log equal in magnitude to the force applied by the log to the sled.
   
   
5. Once the sled has stopped, the child walks to the front of the sled in an attempt to touch the log. How will she move, relative to the stationary log?
   1. She will move forward, as fast as she would on dry ground because the sled is rough.
   2. She will move forward, but not as fast as she would on dry ground.
   3. She will not move at all, because the ice is frictionless.
   4. She will move backward, because the sled will move forward.
   
   
6. If the child needs to get back to her starting point, which of the following would allow her to do this?
   1. Walking to the back of the sled and sitting down.
   2. Walking back and forth in the sled as fast as she can.
   3. Throwing her oversized hat away from the sled.
   4. Any of the above.
   
   
7. As the sled moves back to the starting point, it is observed to slow down. Which of the following statements is TRUE about the child/sled system?
   1. Momentum is not conserved; kinetic energy is conserved.
   2. Momentum is not conserved; total energy is not conserved.
   3. Momentum is conserved; kinetic energy is not conserved.
   4. Momentum is conserved; total energy is conserved.
   
   

Quantitative I:

Complete these end-of-chapter problems (not questions!) from your textbook, submitting only your final circled choice for an answer.

Chapter 7.

42a.

42b.

46.

54. Assume the horizontal component of the velocity of the stone is in the +x direction.

Quantitative II:

Chapter 7, problems 29, 32.

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