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solution_pdf8 - magalhaes(bam2734 Homework#6 Erskine(58200...

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magalhaes (bam2734) – Homework #6 – Erskine – (58200) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Which of the statements A. The energy stored in food is one kind of potential energy; B. The motion of an object looks different to observers in the same frame of reference; C. Two cars moving at the same velocity have different amounts of kinetic energy if one car has more mass than the other car. is/are true? 1. A only 2. None is true. 3. C only 4. A and B only 5. B and C only 6. A and C only correct 7. All are true. 8. B only Explanation: Motion looks the same to observers in the same frame to reference. 002 10.0 points An example of stored chemical energy is 1. an electric motor. 2. the sun’s energy. 3. gasoline in an automobile. correct 4. light. Explanation: 003 10.0 points Heat energy is associated with 1. motion. 2. the internal motion of particles of matter. correct 3. position or shape. 4. holding together the nuclei of atoms. Explanation: 004 10.0 points Chemical energy is 1. contained in the nuclei of atoms. 2. energy that bonds atoms or ions together. correct 3. a result of the internal motion of particles of matter. 4. a result of the motion of electric charges. Explanation: 005 10.0 points This question is typical on some driver’s li- cense exams: A car moving at 46 km / h skids 13 m with locked brakes. How far will the car skid with locked brakes at 138 km / h? Correct answer: 117 m. Explanation: 138 km / h 46 km / h = 3 At 3 times the speed, it has 9 times the KE parenleftbigg 1 2 m v 2 parenrightbigg and will skid 9 times as far: 117 m. Since the frictional force is about the same in both cases, the distance has to be 9 times as great for 9 times as much work done by the pavement on the car. 006 10.0 points
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magalhaes (bam2734) – Homework #6 – Erskine – (58200) 2 You do a certain amount of work on an object initially at rest, and all the work goes into increasing the object’s speed. If you do work W , suppose the object’s final speed is v . What will be the object’s final speed if you do twice as much work? 1. 2 v correct 2. 2 v 3. 4 v 4. v 2 5. Still v Explanation: W = Δ K = 1 2 m v 2 v 2 so W v 2 and v 2 v 2 = 2 W W v = 2 v . 007 10.0 points Two identical objects are moving directly to- ward one another at the same speed v . vectorv - vectorv m m What is the total kinetic energy of the sys- tem of the two objects? 1. Zero since ( vectorv - vectorv ) 2 = 0 2. 4 m v 2 since (2 v ) 2 = 4 v 2 3. Still 1 2 m v 2 from the definition of kinetic energy 4. None of these 5. m v 2 since energy is a scalar correct Explanation: Since kinetic energy is an additive scalar, the total kinetic energy of the system of two objects is 1 2 m v 2 + 1 2 m v 2 = m v 2 . 008 10.0 points A 0 . 39 kg mass is initially at rest and is free to move with negligible friction along the x - axis. The figure below shows the value of an applied force as a function of time.
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