Transcript Work

WORK
Work changes the energy of a
system by applying an external
force through a displacement (x).
W = F•r = Fxcos = F// x
Units: Nm = Joule (J)
W = Work
F// = The force parallel
to the displacement
x = displacement
F

Fcos=F
x//
Δx
Graphically work is equal to the
area under the graph of force (F)
vs. position (x).
F (N)
Work
(Energy)
x (m)
Example 1: Calculate the work
done by the 20N force.
20N
5m
W = Fx cos = (20N)(5m)(cos 0) = 100 Nm
Example 2: Calculate the work
done by the 20N force.
30
5m
W = Fx cos = (20N)(5m)(cos 30) = 86.6 Nm
Example 3: Calculate the work
done by the 20N force.
20N
5m
Fg
W = Fx cos = (20N)(5m)(cos 90) = 0 Nm
Example 4: Calculate the work
done by the 20N force.
30
W = Fx cos = (20N)(5m)(cos 0) = 100 Nm
Example 5: A rope applies a tension of 400N to a 35kg
crate. Assuming the crate starts from rest find the velocity
of the crate after being raised 5 meters. (Neglect friction)
E0  W  E f
W  K Ug
400N
1 2
F// x  mv  mgh
2
1
2
(400)(5)  (35)v  (35)(10)(5)
2
2000  17.5v  1750
2
5m
250  17.5v 2
14.3  v
2
m
v  3 .8
s
35kg