Moment of a Couple Part A Learning Goal: To be able to calculate couple moments.

Question

Moment of a Couple Part A Learning Goal: To be able to calculate couple moments. A couple is defined as two parallel forces, separated by a distance, that have equal magnitudes but opposite directions. A couple only produces a rotation in a specified direction. The moment produced by a couple is called a couple moment. As shown, a submarine hatch door is to be opened by applying two oppositely oriented forces of equal magnitude F 70.0lb at points A and 8 on the hatch door wheel. The radii of the wheets inner and outer rings are ri-1.90 ft and r2 = 0.700 ftrespectively (Figure1) Calculate the moments MA and Mp about point D for the forces applied at points A and B. Then, determine the resulting couple moment MR. Assume that a rotation whereas a negative moment produces a clockwise rotation s a cou Express your answers numerically in pound-feet to three significant figures separated by commas Hints vec lb ft Figure 1 of 1 Submit My Answers Give Up Part B This question will be shown after you complete previous question(s) Part C This question will be shown after you complete previous question(s) Continue

Explanation / Answer

F=70 lb

r1=1.9 ft

r2=0.7 ft

The force at A does not create any moment about A

Hence we can say that MA=0

The force at B is 70 N and has a moment arm about A equal to the diameter of the wheel MB=Fx(2r1)=70x2x1.9=81.07 Newton ( converted ft to meters)

MR=-MA+MB=81.07 Newtons

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