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Y06 ch6
1
Work (
Ch. 6)
Main ideas and results:
•
Wo r k o f a
constant force
F
along a
straight path
W
=
F
·
s
=
Fs
cos
θ
SI unit:
1
joule;
Sign of work
;wo
rko
f
sum of forces
equals sum of
works
W
F
1
+
F
2
=
W
F
1
+
W
F
2
•
Work along a curve
C
:
W
=
W
C
F
=
Z
C
F
·
d
l
=
Z
C
F
·
d
s
=
Z
C
F
cos
θ
ds,
If the path
C
is split into two parts,
C
1
and
C
2
,then
W
C
F
=
W
C
1
F
+
W
C
2
F
•
Workenergy theorem
(for motion under the force
F
):
work equals to change in kinetic energy
W
F
=
K
2
−
K
1
,
where, for a point mass, its
kinetic energy
is
K
=
1
2
mv
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2
•
Power
is the
time rate
at which the work is performed
P
av
=
∆
W
∆
t
→
P
inst
=
dW
dt
as
∆
t
→
0
SI units: watt = joule/sec, horsepower
1 hp = 550 ft
/
(lb
·
s) =
746 W
Power delivered by force
F
acting on a body moving
with velocity
v
:
P
=
F
·
v
Y06 ch6
3
•
Sign of work
. Consider
What is the sign of the work done by the force
F
1
,
F
7
,
F
5
on displacement
s
?
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4
¨
A constant external force
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This note was uploaded on 03/19/2008 for the course PHYS 2305 taught by Professor Tschang during the Spring '08 term at Virginia Tech.
 Spring '08
 TSChang
 Physics, Force, Work

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