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4–6. If , determine the moment produced by the 4-kN force about point A.

u = 45° 3 m

0.45 m

4 kN

A

u

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4–14. Serious neck injuries can occur when a footballplayer is struck in the face guard of his helmet in themanner shown, giving rise to a guillotine mechanism.Determine the moment of the knee force aboutpoint A. What would be the magnitude of the neck force Fso that it gives the counterbalancing moment about A?

P = 50 lb2 in.

4 in.

6 in.30�

60�

P � 50 lb

F

A

4–15. The Achilles tendon force of ismobilized when the man tries to stand on his toes. As this isdone, each of his feet is subjected to a reactive force of

Determine the resultant moment of and about the ankle joint A.

NfFtNf = 400 N.

Ft = 650 N

100 mm65 mm

200 mm

A

Nf � 400 N

Ft

5�

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4–30. If and determine the resultantmoment about the bolt located at A.

FC = 45 lb,FB = 30 lb

4–31. The rod on the power control mechanism for abusiness jet is subjected to a force of 80 N. Determine themoment of this force about the bearing at A.

20�

60�

A80 N

150 mm

*4–32. The towline exerts a force of at the endof the 20-m-long crane boom. If determine theplacement x of the hook at A so that this force creates amaximum moment about point O. What is this moment?

u = 30°,P = 4 kN

1.5 m

O

20 m

A

B

P � 4 kN

x

u

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4–26. The foot segment is subjected to the pull of the twoplantarflexor muscles. Determine the moment of each forceabout the point of contact A on the ground.

60�

30�

4 in.

A1 in.

3.5 in.

70�

F2 � 30 lb

F1 � 20 lb

4–27. The 70-N force acts on the end of the pipe at B.Determine (a) the moment of this force about point A, and(b) the magnitude and direction of a horizontal force, appliedat C, which produces the same moment.Take u = 60°.

A

C0.3 m 0.7 m

0.9 m

B

70 N

u

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•4–21. Determine the direction for of theforce F so that it produces the maximum moment aboutpoint A. Calculate this moment.

0° … u … 180°u F � 400 N

3 m

2 m

A

u

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4–34. In order to hold the wheelbarrow in the positionshown, force F must produce a counterclockwise momentof about the axle at A. Determine the requiredmagnitude of force F.

200 N # m B

0.65 m

0.5 m

1.2 m

30�

0.3 m

F

G

A

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4–35. The wheelbarrow and its contents have a mass of50 kg and a center of mass at G. If the resultant momentproduced by force F and the weight about point A is to bezero, determine the required magnitude of force F.

B

0.65 m

0.5 m

1.2 m

30�

0.3 m

F

G

A

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