1
A
65kg
person
stands
on
a
lightweight ladder (the weight of the
ladder is negligible).
The floor is rough; hence it exerts
both
a
normal
force
F
N
,
and
a
frictional force
f
, on the ladder.
The
wall,
on
the
other
hand,
is
frictionless; it exerts only a normal
force
P
on the ladder.
Find the magnitudes of
P
,
F
N
and
f
.
W
P
F
N
f
W
Weight of the person:
N
s
m
kg
mg
W
637
)
/
8
.
9
)(
65
(
2
Static Equilibrium: Example in
Textbook p.346
P
F
N
f
W
0
,
0
,
0
y
x
F
F
Force
xcomp
ycomp
P
P
0
W
0
637N
F
N
0
F
N
f
f
0
0
f
P
F
x
0
637
N
y
F
F
N
F
N
637
Choose bottom of the ladder as rotational axis
Torque by F
N
= 0, Torque by f = 0
Force
lever arm
torque
P
l
for
P
W
m
7
.
0
m
8
.
3
P
m
)
8
.
3
(
Nm
N
m
446
)
637
)(
7
.
0
(
+: counterclockwise

: clockwise
0
446
8
.
3
P
N
P
117
0
f
P
F
x
N
f
117
(about
any
axis)
l
for
W
F
N
m
0
0
f
m
0
0
(force
F
N
goes through axis)
(force
f
goes through axis)
Plug
into:
N
P
117
Solutions:
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