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Work - Transfer of energy

F. Fcos . . s. Work - Transfer of energy. Work = (Force)(Distance) W = Fs cos . F. Fcos . . s. W = Fs cos . Tricky bits : 0 o cos  = 1 180 o cos  = -1 (examples of positive, negative work).

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Work - Transfer of energy

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  1. F Fcos  s Work - Transfer of energy Work = (Force)(Distance) W = Fs cos

  2. F Fcos  s W = Fs cos Tricky bits : 0o cos = 1 180ocos = -1 (examples of positive, negative work)

  3. Ex1 - Fred O’Dadark exerts 13.2 N on a rope that makes a 32o angle with the ground, sliding a sled 12.5 m along the ground. What work did he do? W = Fs cos = (13.2 N)(12.5 m) cos(32o) = 139.9 Nm = 139.9 Joules = 140 J 140 J

  4. Ex2 - Jane Linkfence does 132 J of work lifting a box 1.56 m. What is the weight of the box? W = Fs cos  = 0o (assuming she lifts straight up) W = Fs, F = W/s = (132 Nm)/(1.56 m) = 84.6 N 84.6 N

  5. Ex3 - Helena Handbasket brings a 5.2 kg box down from a 1.45 m tall shelf. What work does she do? (3 hints) F = ma, weight = mg W = Fs cos  = 180o (tricky tricky) F = (5.2 kg)(9.81 N/kg) = 51.012 N W = Fs cos(180o) = (51.012 N)(1.45 m) cos(180o) = -73.9674 J = -74 J (The box does work on her. gives her energy) -74 J

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