A 14.5-m uniform ladder weighing 485 N rests against a frictionless wall. The ladder makes a 63.0° angle with the horizontal. (a) Find the horizontal and vertical forces the ground exerts on the base of the ladder when an 845-N firefighter has climbed 3.74 m along the ladder from the bottom. (b) If the ladder is just on the verge of slipping when the firefighter is 8.75 m from the bottom, what is the coefficient of static friction between ladder and ground?

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12.1

A 14.5-m uniform ladder weighing 485 N rests against a frictionless wall. The ladder makes a 63.0° angle with
the horizontal.
(a) Find the horizontal and vertical forces the ground exerts on the base of the ladder when an 845-N
firefighter has climbed 3.74 m along the ladder from the bottom.
(b) If the ladder is just on the verge of slipping when the firefighter is 8.75 m from the bottom, what is
the coefficient of static friction between ladder and ground?
Transcribed Image Text:A 14.5-m uniform ladder weighing 485 N rests against a frictionless wall. The ladder makes a 63.0° angle with the horizontal. (a) Find the horizontal and vertical forces the ground exerts on the base of the ladder when an 845-N firefighter has climbed 3.74 m along the ladder from the bottom. (b) If the ladder is just on the verge of slipping when the firefighter is 8.75 m from the bottom, what is the coefficient of static friction between ladder and ground?
(a) The wall is frictionless, but it does exert a horizontal normal force nw. For the x and y components of the
force, we have the following from Newton's second law.
Fx = fs - nw = 0
Fy = ng-
845
Taking torques about an axis at the foot of the ladder, we have the following.
Στι
τ = 0
nw
=
=
845
= ( 8
+(485 N)(0
The correct answer is not zero. m sin 27°
- nw(
n. 14.5
nw'
=
Solving this equation for
[(3.74 m)
The correct answer is not zero. m
we have
N
835
14.5
- 485 N = 0
N) (3.74 m)
X
3.74 m sin 27°
m
cos 27°
N+ 0
m) (485 N)]
N.
Next substitute the value for nw into the Fx equation to find
W
fs="w
n
N.
The friction force is in the positive x direction toward the wall.
m
X
tan 27°
Transcribed Image Text:(a) The wall is frictionless, but it does exert a horizontal normal force nw. For the x and y components of the force, we have the following from Newton's second law. Fx = fs - nw = 0 Fy = ng- 845 Taking torques about an axis at the foot of the ladder, we have the following. Στι τ = 0 nw = = 845 = ( 8 +(485 N)(0 The correct answer is not zero. m sin 27° - nw( n. 14.5 nw' = Solving this equation for [(3.74 m) The correct answer is not zero. m we have N 835 14.5 - 485 N = 0 N) (3.74 m) X 3.74 m sin 27° m cos 27° N+ 0 m) (485 N)] N. Next substitute the value for nw into the Fx equation to find W fs="w n N. The friction force is in the positive x direction toward the wall. m X tan 27°
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