Homework 5 1) Show that the gravitational potential energy of a 1000-kg boulder raised 5 m above ground level is 50,000 J. (You can express g in units of N/kg because m/s2 is equivalent to N/kg.) 2) Show that the kinetic energy of a 1.0-kg book tossed across the room at a speed of 3.0 m/s is 4.5 J. (1 J is equivalent to 1 kg-m/s2.) 3) The second floor of a house is 6 m above the street level. How much energy will have to be spent to lift a 300-kg refrigerator to the second-story level from the street level? 4) This question is typical on some driver's license exams: A car that was moving at 50 km/h skids 15 m with locked brakes. How far will the car skid with locked brakes if it was moving at 150 km/h? 5) Belly-flop Bernie dives from atop a tall flagpole into a swimming pool below. His potential energy at the top is 10,000 J (relative to the surface of the pool). What is his kinetic energy when his potential energy is reduced to 1000 J? Ignore the presence of air-resistance in your answer. 6) Ranking Question: The roller coaster ride starts from rest at point A. Rank these quantities from greatest to least at each point: a. Speed b. KE c. PE 7) A physics instructor demonstrates energy conservation by releasing a heavy pendulum bob, as shown in the sketch, and allowing it to swing to and fro. What would happen if, in his exuberance, he gave the bob a slight shove as it left his nose? Explain. 8) Suppose that you and two classmates are discussing the design of a roller coaster. One classmate says that each summit must be lower than the preceding one. Your other classmate says this is nonsense, for as long as the first one is the highest, it doesn't matter what height the others are. What do you say? 9) What famous equation by Albert Einstein describes the relationship between mass and energy? 10) Which, if either, has greater kinetic energy: a 1-kg ball moving at 2 m/s or a 2-kg ball moving at 1 m/s? 11) In the absence of air resistance, a ball thrown vertically upward with a certain initial KE will return to its original level with the same KE. When air resistance is a factor affecting the ball, will it return to its original level with the same, less, or more KE? Does your answer contradict the law of energy conservation? 12) When the speed of a moving car is doubled, how much more kinetic energy does it have? 13) What is the source of energy of sunshine