WorkContents:

•Definition•Tricky Bits•Whiteboards

Work - Transfer of energy

Work = (Force)(Distance)

W = Fs cos

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F

s

Fcos

W = Fs cos

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Tricky bits : 0o cos = 1180o cos = -1(examples of positive, negative work)

F

s

Fcos

Whiteboards: Work

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140 J W

W = Fs cos = (13.2 N)(12.5 m) cos(32o) = 139.9 Nm= 139.9 Joules = 140 J

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?

So a Nm = J (Joule)

84.6 N W

W = Fs cos = 0o (assuming she lifts straight up)W = Fs, F = W/s = (132 Nm)/(1.56 m) = 84.6 N

Jane Linkfence does 132 J of work lifting a box 1.56 m. What is the weight of the box?

2.5 m W

W = Fs cos = 0o (assume)W = Fs, s = W/F = (108 Nm)/(43 N) = 2.5 m

Bobbie Sachs exerts 43 N of force, and does 108 J of work pushing a sofa how far? (2 hints)

-74 J W

F = ma, weight = mgW = Fs cos = 180o (tricky tricky)F = (5.2 kg)(9.8 N/kg) = 50.96 NW = Fs cos(180o) = (50.96 N)(1.45 m) cos(180o) = -73.892 J = -74 J(The box does work on her. gives her energy)

Helena Handbasket brings a 5.2 kg box down from a 1.45 m tall shelf. What work does she do? (3 hints)