PHY231 lecture8 - Physic 231 Lecture 8 Main points of...

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Physic 231 Lecture 8 Main points of today’s lecture: Potential energy of spring 2 1 E Work, energy and non- conservative and external 2 kx PE = forces f0 f 0 KE KE PE W −+ + •P o w e r nonconservative ext WW =+ v F P W P = = ; t Δ
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Example A water slide is constructed so that swimmers, starting from rest at the top of the slide, leave the end of the slide traveling horizontally. As the drawing shows, one person is observed to hit the water 5.00 m from e end of the slide in a time of 0 500 s after leaving the slid Ignoring the end of the slide in a time of 0.500 s after leaving the slid. Ignoring friction and air resistance, find the height H in the drawing. s m s m t x v t v x f f : slide of bottom at height h / 10 5 . 0 5 ; = = = Δ = = Δ () m s s m h gt : energy of on Conservati 23 . 1 5 . 0 ) / 9 . 4 ( 2 1 h - 2 2 = = = m g v h H h H mg mv 33 . 6 2 ; 2 1 2 2 = + = =
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Conceptual problem Two marbles, one twice as heavy as the other, are dropped to the ground from the roof of a building. Just before hitting the ground, the heavier marble has – a) as much kinetic energy as the lighter one. – b) twice as much kinetic energy as the lighter one. – c) half as much kinetic energy as the lighter one. – d) four times as much kinetic energy as the lighter one. – e) impossible to determine
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clicker question 0 400 g bead slides on a curved wire starting from rest at point A 0.400-kg bead slides on a curved wire, starting from rest at point A in the figure below. If the wire is frictionless, find the speed of the bead at C . A C B ) y y ( mg PE PE KE PE KE PE KE f 0 f 0 f 0 0 f f = = + = + – a) 5.2 m/s ) 1.4 m/s s / m 7 . 7 ) y y ( g 2 v ) y y ( mg mv 2 1 f 0 f f 0 2 f = = = b) 1.4 m/s – c) 23 m/s – d) 7.7 m/s
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PHY231 lecture8 - Physic 231 Lecture 8 Main points of...

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