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Work and Energy Part 2

Work and Energy Part 2. Mechanical Energy is usually conserved in the absence of friction. The 80 kg Mr. Schoettle is at the top of a 10 m slide. How fast will he be going at the bottom?. ME i = ME f. PE i + KE i = PE f + KE f. 0. 0. (mgh) i + ½mv 2 i = (mgh) f + ½ mv 2 f.

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Work and Energy Part 2

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  1. Work and Energy Part 2

  2. Mechanical Energy is usually conserved in the absence of friction

  3. The 80 kg Mr. Schoettle is at the top of a 10 m slide. How fast will he be going at the bottom? MEi = MEf PEi + KEi = PEf + KEf 0 0 (mgh)i + ½mv2i = (mgh)f + ½mv2f (mgh)i = ½mv2f vf = 14 m/s

  4. Work-Kinetic Energy Theorem Wnet = DKE net work = change in kinetic energy

  5. If the block starts to slide, what will be the speed at the bottom? mk = 0.55 N f 1000 kg Wnet = DKE =Fnet d h = 30 m F ׀׀=sin 40°mg mg = 1000 kg (9.81 m/s2 ) F ﬩ f = mN = mF ﬩ = mmg(cos40°) 40° F׀׀ Fnet = sin 40°mg - mmg(cos40°) = 2173 N d = sin 40°h = (sin 40°)-1 30 m = 46.7 m W = Fnetd = (2173 N) 46.7 m = 101458 J Wnet = 101458 J = DKE = ½mv2 v = 14.2 m/s

  6. Power How fast work is done P = W/Dt P = Fv

  7. Oops! I carry the heavy triangle up the stairs in 7.5 s…..how powerful am I? F = mg = 50 kg (9.81 m/s2) F = 490.5 N 50 kg 7m W = Fd = (490.5 N) 7 m W = 3433.5 J P = W/Dt = 3433.5 J / 7.5 s P = 457.8 W

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