ENERGY AND ITS CONSERVATION Understanding Physics Concepts For each statement below, write true or rewrite the italicized part to make the statement true. 1. 2. 3. 4. 5. A When you throw a ball into the air, mechanical energy at any point is the difference in the kinetic energy and gravitational potential energy. As an object falls towards Earth, the gravitational potential energy of the object-Earth system increases. The total amount of energy of an isolated, closed system remains constant. If a tabletop is used as a reference point in a mechanical-energy problem, the gravitational potential energy for an object on the floor is greater than zero. Of the three sets of bar graphs below, an inelastic collision is represented by graph A. B C Kafter thermal Katter Kbefore Kbefore For each term on the left, write the letter of the matching item. 6. KEtrans 7. GPE 8. 1 joule Kbefore 9. result of an elastic collision Kafter a. KE after =KE before b. = mgh C. =Im d. 1 kgm/s Thinking Critically Answer the following questions. Show your calculations. 1. Under what conditions will a 0.030-kg marble-Earth system and a 3.00-kg rock-Earth system have the same gravitational potential energy? Do not use the case where both objects are at the reference level. 2. Under what conditions will a moving 0.030-kg marble and a moving 3.00-kg rock have the same translational kinetic energy? Do not use the case where both objects are stationary. 3. 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? Answer the following questions. Show your calculations. 10. Determine the mechanical energy for 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. 11. Compare the kinetic energies for a biker and bike (with a combined mass of 80.0 kg) traveling at 3.00 m/s and the same biker and bike traveling twice as fast. 12. Which has the greater gravitational potential energy-a flower pot-Earth system with a 550-g flower pot sitting on a 1.2-m high shelf or a flower pot-Earth system with a 350-g flower pot sitting on a 1.8-m high shelf? 13. 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-Earth system? 14. 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 from their motion, how fast are they moving?