PHY 121 Ch 6b Lecture

PHY 121 Ch 6b Lecture - 1 Lecture 11 Thursday February 21 2...

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Unformatted text preview: 1 Lecture 11 Thursday, February 21 2 The work done by a force A. is the area under the force versus position graph. B. is the slope of the force versus position graph. C. is the area under the force versus velocity graph. D. is the product of force times velocity. 3 Hooke’s law... A. states that the magnitude of the spring force is proportional to the displacement from equilibrium. B. states that the magnitude of the spring force is inversely proportional to the displacement from equilibrium. C. states that the magnitude of the spring force is constant if the displacement is not too large. D. is not discussed in the reading assignment. 4 The unit of power is called A. Watt B. Joule C. Newton D. Coulomb 5 An object moves along a curved path. A. Only the component of the force perpendicular to the path can change the kinetic energy. B. Only the component of the force parallel to the path can change the kinetic energy. C. Both components of the force can change the kinetic energy. D. None of the components of the force can change the kinetic energy. 6 Work by a variable force • We defined work as • This definition only makes sense if the force is constant during the motion. Otherwise, we don’t know what value of the force to use. W = ! F ! ! s = F x " x + F y " y • Solution: divide up the trajectory into little segments. Calculate the work for each segment, add up the partial works. 7 Variable forces: the spring force F sp ( ) x ! kx This is the spring constant 8 Work by the spring force W = !...
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PHY 121 Ch 6b Lecture - 1 Lecture 11 Thursday February 21 2...

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