Things you knew & should remember (in the onslaught of new
material) going into Exam 2:
The fundamental definition of work is
f
i
r
r
W
F dr
=
⋅
∫
G
G
G
G
Hence to get the work done on an object by
, first consider the
direction of the displacement
and the
direction of the force
during the trajectory. If
for the entire trajectory
Where
F dr
Fdrcos
⋅
=
φ
G
G
dr
G
F
G
φ
dr
G
F
G
dr
G
F
G
0
φ =
Work done
is positive
dr
G
F
G
o
180
φ =
Work done
is negative
W
F r
=
Δ
W
F r
= − Δ
dr
G
F
G
o
90
φ =
Work done
is zero
W
0
=
F
G

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