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# C5 - Applied Science Department(ASD Centre for Foundation...

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FOSEE , MULTIMEDIA UNIVERSITY (436821-T) MELAKA CAMPUS, JALAN AYER KEROH LAMA, 75450 MELAKA, MALAYSIA. Tel 606 252 3594 Fax 606 231 8799 URL: http://fosee.mmu.edu.my/~asd/ PPH0075 Physics 1 Foundation in Engineering ONLINE NOTES Chapter 5 Work and Energy Applied Science Department (ASD) Centre for Foundation Studies and Extension Education (FOSEE)

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PPH0075 Physics 1 Chapter 5 ______________________________________________________________________________________ ASD 2008/09 1/ 11 Chapter 5 Work and Energy Work Energy Work done by Constant Force Work done by Varying Force Work done by Conservative Force Work done by non- Conservative Force Work-Energy Theorem Power and Efficiency of System Conservation of Energy Kinetic Energy Potential Energy
PPH0075 Physics 1 Chapter 5 ______________________________________________________________________________________ ASD 2008/09 2/ 11 5.1 Definitions a) WORK : Work is done by a force acting on an object when the point of application of that force moves through some distance and the force has a component along the line of motion . The symbol is W. The unit is Newton Meter (Nm) or Joule (J) b) ENERGY : The ability to do work. c) KINETIC ENERGY : Energy associated with the motion of an object The symbol is K. The unit is J d) POTENTIAL ENERGY : Energy associated with the position or configuration of an object Example : Gravitational potential energy (U = mgh) & Elastic (spring) potential energy (U = 2 m kx 2 1 ). The symbol is U and the unit is J. 5.2 Work Done by a Constant Force Consider a particle that undergoes a displacement s along a straight line while acted on by a constant force F , which makes an angle θ with s as shown in the diagram The work W done by an agent exerting a constant force is the product of the component of the force in the direction of the displacement and the magnitude of the displacement of the force, i.e. Where F and s are the magnitudes of the force vector F and displacement vector s and θ is the angle between these vectors. W = F . s = F s cos θ

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PPH0075 Physics 1 Chapter 5 ______________________________________________________________________________________ ASD 2008/09 3/ 11 The angle θ in the work definition is the angle between the force vector and displacement vector, which is not always the angle from the horizontal. From the work definition : (a) A force does no work on a particle if the particle does not move . If s = 0, ° W = Fs cos θ = 0 (b) The work done by a force is zero when the force is perpendicular to the displacement. If F s , then θ = 90 0 , ° W = Fs cos θ = Fs cos 90 0 = 0 For the above diagram : W n = ns cos 90 0 = 0 W F = Fs cos θ W f = fs cos 180 0 = -fs W mg = mgs cos 270 0 = 0 (c) The sign of the work depends on the direction of F relative to s .
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C5 - Applied Science Department(ASD Centre for Foundation...

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