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Physics October-17-08

# Physics October-17-08 - x = 0 – 15(cos50 o – 12(cos30 o...

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Physics October-17-08 Kinetic Energy and Work A force does positive work when it has a vector component in the same direction as the displacement. A force does negative work when it has a vector component in the opposite direction of the displacement. Finally, a force does no work when the force and displacement are perpendicular to one another. F net
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Unformatted text preview: x = 0 – 15(cos50 o ) – 12(cos30 o ) = -20 F net y = 10 + 15(sin50 o ) – 12(sin30 o ) = 15.5 F net = (F net x 2 + F net y 2 )-1/2 = 25.3N Ø = tan-1 (15.5/20) = 142 o (2 nd quadrant) W = F net d cos Ø = (25.3) (0.4) cos (0 o )= 10.1J Work energy Theorem: ΔK = K f – K i = ∑W-K f = m v i 2 /2 + net work-W g = m g cos(0 o ) = m g...
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