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Work-Energy Principle

Work-Energy Principle. Conservation of Mechanical Energy. Work done = Change in K.E. + Change in PE.

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Work-Energy Principle

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  1. Work-Energy Principle Conservation of Mechanical Energy Work done = Change in K.E. + Change in PE A rough slope is inclined at tan-1( ¾ ) to the horizontal. A box of mass 25 kg slides from rest a distance of 20 m down a line of greatest slope, at which point it has developed a speed of 14 m/s. Find the work done against friction and the coefficient of friction. Gain in K.E. = 0.5 25  142 = 2450 Loss in P.E. = 25 9.8  20  3/5 = 2940 Loss in energy = 490 = WD against friction

  2. Work-Energy Principle Loss in energy = 490J = WD against friction WD = Fd Friction = 490  20 = 24.5 N  = 24. 5  259.8(4/5) = 0.125

  3. Work-Energy Principle A bullet of mass 20 grams is fired horizontal into a vertical target of 15 cm thickness with a speed 250 m/s. If the target offers a resistance of 3600N, with what speed will the bullet emerge on the far side? K.E. = 0.5 0.020  2502 = 625 J WD against resistance = 3600 0.15 = 540 J Energy level on far side = 85 v = 92.2 m/s

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