hw9 - lavallo (jhl936) Homework 09 orin (58140) This...

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lavallo (jhl936) – Homework 09 – forin – (58140) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices be±ore answering. 001 10.0 points An object hangs motionless ±rom a spring. When the object is pulled down, the sum o± elastic potential energy o± the spring and the gravitational potential energy o± the object and Earth 1. increases. correct 2. stays the same. 3. decreases. Explanation: I± released ±rom its new position, the object accelerates upward and passes the equilibrium point with nonzero velocity. The two ±orms o± potential energy are elastic potential en- ergy o± the spring and gravitational potential energy. Even though the latter decreases as the object is pulled down, the sum o± the two must increase ±or the object to be able to gain kinetic energy. 002 10.0 points A conservative ±orce has the potential energy ±unction U ( x ), shown by the graph. A particle moving in one dimension under the infuence o± this ±orce has kinetic energy 1.0 Joule when it is at position x 1 . x 0 x 1 x 2 x 3 1 0 1 Position Potential Energy (J) Potential Energy vs Position Which o± the ±ollowing is a correct state- ment about the motion o± the particle? 1. It cannot reach either x 0 or x 2 . 2. It comes to rest at either x 0 or x 2 . 3. It moves to the right o± x 3 and does not return. 4. It moves to the le±t o± x 0 and does not return. 5. It oscillates with maximum position x 2 and minimum position x 0 . correct Explanation: The total energy o± the particle is con- served, since only a conservative ±orce 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 o± the particle.
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This note was uploaded on 04/09/2010 for the course PHY 58150 taught by Professor Florin during the Spring '10 term at University of Texas.

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hw9 - lavallo (jhl936) Homework 09 orin (58140) This...

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