Phys 0174 Fall 2008 - Chapter 07, 4 slides

Phys 0174 Fall 2008 - Chapter 07, 4 slides - Chapter 7...

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Chapter 7 Kinetic Energy and Work ¾ Kinetic energy ¾ Work done by a force ¾ Work-Kinetic Energy Theorem ¾ Power m m Kinetic Energy Kinetic energy K is defined as: 2 1 2 Km v = Work: (symbol W) If a force F is applied to an object of mass m it can accelerate it and increase its speed v and kinetic energy K . Similarly F can decelerate m and decrease its kinetic energy. We account for these changes in K by saying that F has transferred energy W to or from the object. If energy it transferred to m (its K increases) we say that work was done by F on the object ( W > 0). If on the other hand energy its transferred from the object (its K decreases) we say that work was done by m ( W < 0)
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m m Consider a bead of mass that can move without friction along a straight wire along the Finding an expr x-axis. A cons ession for Work done by a constant f tant force applied at an angle or to t c: h e m φ F G e wire is acting on the bead. 22 Apply Newton's second law: Assume that the bead has an initial velocity and after it has travelled a distance its velocity is . Apply the constant acceleration equation: 2 xx o ox Fm a vv a = −= v dv G G G Multiply both sides by 2 2 2 cos 222 2 and cos Thus the work done the force the bead is give by n by: cos on x x io f f i x d m F mmm m vv a d d F d Fd m mm KvK v K K F d WW F d F d = = = == = cos WF d = W =⋅ GG m m Note 1: Note 2: The unit of is the same as that of i.e.
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Phys 0174 Fall 2008 - Chapter 07, 4 slides - Chapter 7...

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