Homework #6-solutions

# Homework #6-solutions - nichols (scn285) – Homework #6...

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Unformatted text preview: nichols (scn285) – 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. Two cars moving at the same velocity have different amounts of kinetic energy if one car has more mass than the other car; B. The motion of an object looks different to observers in the same frame of reference; C. The energy stored in food is one kind of potential energy. is/are true? 1. All are true. 2. None is true. 3. A and C only correct 4. B only 5. A and B only 6. C only 7. B and C only 8. A 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. light. 2. gasoline in an automobile. correct 3. an electric motor. 4. the sun’s energy. Explanation: 003 10.0 points Heat energy is associated with 1. position or shape. 2. the internal motion of particles of matter. correct 3. motion. 4. holding together the nuclei of atoms. Explanation: 004 10.0 points Chemical energy is 1. a result of the internal motion of particles of matter. 2. energy that bonds atoms or ions together. correct 3. a result of the motion of electric charges. 4. contained in the nuclei of atoms. Explanation: 005 10.0 points This question is typical on some driver’s li- cense exams: A car moving at 45 km / h skids 15 m with locked brakes. How far will the car skid with locked brakes at 135 km / h? Correct answer: 135 m. Explanation: 135 km / h 45 km / h = 3 At 3 times the speed, it has 9 times the KE 1 2 mv 2 and will skid 9 times as far: 135 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 nichols (scn285) – 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. 4 v 2. 2 v 3. √ 2 v correct 4. v √ 2 5. Still v Explanation: W = Δ K = 1 2 mv 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 . v- v m m What is the total kinetic energy of the sys- tem of the two objects? 1. None of these 2. mv 2 since energy is a scalar correct 3. Still 1 2 mv 2 from the definition of kinetic energy 4. Zero since ( v- v ) 2 = 0 5. 4 mv 2 since (2 v ) 2 = 4 v 2 Explanation: Since kinetic energy is an additive scalar, the total kinetic energy of the system of two objects is 1 2 mv 2 + 1 2 mv 2 = mv 2 ....
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## This note was uploaded on 04/06/2010 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.

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Homework #6-solutions - nichols (scn285) – Homework #6...

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