Chapter Assessment Use with Chapter 11.

Transcription

1 Date Period 11 Use with Chapter 11. Energy Understanding Concepts Part A For each of the statements below, write true or rewrite the italicized part to make the statement true. 1. When you throw a ball into the air, its mechanical energy at any point is the difference in its kinetic energy and gravitational potential energy. 2. As an object falls towards Earth, the gravitational potential energy of the object increases. 3. The total amount of energy in an isolated, closed system remains constant. 4. If a tabletop is used as a reference point in a mechanical-energy problem, an object lying on the tabletop has a gravitational potential energy greater than zero. 5. Of the four sets of bar graphs below, an inelastic collision is represented by set A. A B C E thermal K after K after K after K before K before K before For each term on the left, write the letter of the matching item. 6. K a. K after = K before 7. U g b. mgh 8. 1 joule c. mv 2 9. work-energy theorem d. 1 kg m 2 /s result of an elastic collision e. Fd K 1 2 Physics: Principles and Problems 49

2 Understanding Concepts Part B Answer the following questions, showing your calculations. 1. Determine the mechanical energy of a 5.0-kg stone perched near the edge of a cliff 25.0 m high. Use the base of the cliff as the reference level. 2. Compare the kinetic energies of a biker and bike (with a combined mass of 80 kg) traveling at 3.00 m/s and the same biker and bike traveling twice as fast. 3. Which has the greater gravitational potential energy a 550-g flower pot sitting on a 1.2-m high shelf or a 350-g flower pot sitting on a 1.8-m high shelf? 4. A weight trainer lifts a 90.0-kg barbell from a stand 0.90 m high and raises it to a height of 1.75 m. What is the increase in the potential energy of the barbell? 5. A child having a mass of 35.0 kg is on a sled having a mass of 5.0 kg. If the child and sled traveling together have a kinetic energy of 260 J, how fast are they moving? 50 Physics: Principles and Problems

3 Applying Concepts Answer the following questions, using complete sentences. 1. Describe the energy changes that take place when the spring of a toy car is wound up and then released. 2. Why must the first hill of a roller-coaster ride be the highest hill? 3. Distinguish between an elastic collision and an inelastic collision. 4. A ball is thrown upward. Describe changes in its mechanical energy, kinetic energy, and gravitational potential energy between the time the ball is released and the time it reaches its maximum height. Physics: Principles and Problems 51

4 5. A block of wood rests on a frictionless surface and is attached to a spring, as shown below. When the spring is neither elongated nor compressed, the center of the block of wood is used as the reference point for the elastic potential energy of the block-and-spring system. The spring is then compressed to the left and released. Describe changes in the mechanical energy, kinetic energy, and elastic potential energy of the system between the time the spring is released and when it reaches its maximum elongation. Reference point 52 Physics: Principles and Problems

5 Answer the following questions, showing your calculations. 6. Under what conditions will a kg marble and a 3.00-kg rock have the same gravitational potential energy other than zero? 7. Under what conditions will a moving kg marble and a moving 3.00-kg rock have the same kinetic energy? 8. During a contest that involved throwing a 7.0-kg bowling ball straight up in the air, one contestant exerted a force of 810 N on the ball. If the force was exerted through a distance of 2.0 m, how high did the ball go from the point of release? Physics: Principles and Problems 53

6 9. A 50.0-kg girl jumps onto a stationary 2.4-kg skateboard at 4.1 m/s. Determine the fraction of the original kinetic energy that was lost due to the inelastic nature of the collision. 10. A 50.0-kg skater and skateboard leaves the right side of the ramp shown below at a speed of 7.0 m/s. If the ramp is frictionless, what was his initial speed down the opposite side of the ramp? 2.0 m 0.4 m 6.0 m 54 Physics: Principles and Problems