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5.48. Set Up:
Use coordinates where
is upward and
is horizontal to the right. The applied force pushes to
the left so the friction force is to the right.
Solve: (a)
The freebody diagram is given in Figure 5.48. The applied force
has been replaced by its
x
and
y
components.
Figure 5.48
(b)
gives
and
(c)
gives
and
(d)
The maximum possible static friction force is
(e)
The vertical component of
F
is now upward.
now gives
5.49. Set Up:
Solve: (a)
must have units of N, so
D
has units
(b)
At the terminal velocity,
and
and
5.50. Set Up:
with
Solve: (a)
At the terminal velocity,
and
and
(b)
5.51. Set Up:
Solve: (a)
At the terminal speed
(b)
When
(c)
When
Reflect:
At the terminal velocity the upward drag force equals the downward gravity force and the acceleration is
zero. At speeds less than
the upward drag force is less than the weight and the person accelerates downward.
5.52. Set Up:
Similar objects have the same size and shape and therefore the same
D
in
For an object of
weight
W
,a
n
d
Solve: (a)
so
(b)
so
(c)
so
v
t
5
"
4
V
T
5
2
V
T
.
D
v
t
2
5
4
W
v
t
5
"
3
V
T
.
D
v
t
2
5
3
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 Spring '07
 Shoberg
 Force, Friction

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