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

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

3. Ex1 - Fred O’Dadark exerts 13
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) = Nm
= Joules = 140 J
140 J

4. Ex2 - Jane Linkfence does 132 J of work lifting a box 1. 56 m
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
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) = N
W = Fs cos(180o) = ( N)(1.45 m) cos(180o)
= J = -74 J
(The box does work on her. gives her energy)
-74 J