PHY 121 Ch 7b Lecture

# PHY 121 Ch 7b Lecture - Lecture 13 Thursday, February 28 1...

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1 Lecture 13 Thursday, February 28

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2 A particle is moving along the x -axis acted on by a conservative force along the x -axis. At a certain point where the force is zero: A. the potential energy is zero. B. the potential energy is greater than zero. C. the potential energy is less than zero. D. not enough information to decide.
3 When looking at a potential energy diagram,one can tell the force…. A. by looking at the slope of the potential energy versus position graph. B. by looking at the area under the potential energy versus position graph. C. by looking at the largest potential energy value. D. It is impossible to tell force from a potential energy diagram.

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4 At a point of stable equilibrium A. the potential energy has a local minimum. B. the potential energy has a local maximum. C. the potential energy has its most negative slope D. none of the above.
5 At a point of unstable equilibrium, the force A. has its largest magnitude. B. is zero. C. points toward a minimum. D. can point in any arbitrary direction.

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6 Conservative or nonconservative? If a force is conservative, it must satisfy ! " ! F = i j k # # x # # y # # z F x F y F z = 0 Example (Problem 7.83): Is (0, - α xy 2 ,0) conservative?
7 The spring force revisited F sp = ! k x ! x 0 ( )

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8 Spring force and spring potential energy 1 2 k x ! x 0 ( ) 2 ! k x ! x 0 ( ) Force is minus the slope of potential F = ! " U " x
9 Energy diagrams I E = K + U K U ! F sp

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10 Energy diagrams II E = K + U K U ! F sp
11 Energy diagrams III E = K + U K U ! F sp

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12 Energy diagrams IV E = K + U K U ! F sp
13 Problem 7.77 A particle with mass m is acted by a conservative force and moves along a path given by x = x 0 cos ω t and y = y 0 sin t , where x 0 , y 0 , and are constants. (a) Find the components of the force that acts on the particle. (b) Find the potential energy of he particle as a function of x and y . Take U = 0 when x =0 and y = 0. (c) Find the total energy of the particle when (i) x = x 0 , y =0, and (ii) x = 0, y = y 0 .

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14 The graph shows the potential
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## This note was uploaded on 10/05/2008 for the course PHY 121 taught by Professor Chamberlin during the Spring '08 term at ASU.

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PHY 121 Ch 7b Lecture - Lecture 13 Thursday, February 28 1...

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