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Unformatted text preview: saldana (avs387) Homework 09 florin (58140) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An object hangs motionless from a spring. When the object is pulled down, the sum of elastic potential energy of the spring and the gravitational potential energy of the object and Earth 1. stays the same. 2. decreases. 3. increases. correct Explanation: If released from its new position, the object accelerates upward and passes the equilibrium point with nonzero velocity. The two forms of potential energy are elastic potential en- ergy of the spring and gravitational potential energy. Even though the latter decreases as the object is pulled down, the sum of the two must increase for the object to be able to gain kinetic energy. 002 10.0 points A conservative force has the potential energy function U ( x ), shown by the graph. A particle moving in one dimension under the influence of this force has kinetic energy 1.0 Joule when it is at position x 1 . x x 1 x 2 x 3 1 1 Position PotentialEnergy(J) Potential Energy vs Position Which of the following is a correct state- ment about the motion of the particle? 1. It comes to rest at either x or x 2 . 2. It moves to the right of x 3 and does not return. 3. It cannot reach either x or x 2 . 4. It oscillates with maximum position x 2 and minimum position x . correct 5. It moves to the left of x and does not return. Explanation: The total energy of the particle is con- served, since only a conservative force acts on it. So at any point on the axis, V ( x ) + U ( x ) = V ( x 1 ) + U ( x 1 ) = 1 . 0 J + ( 1 . 0 J) = 0 , V ( x ) = U ( x ) , where V is the kinetic energy of the particle....
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This note was uploaded on 08/30/2010 for the course PHY 58140 taught by Professor Florin during the Spring '10 term at University of Texas at Austin.
- Spring '10