Express your answer numerically in pound-feet to three significant figures. As s

Question

Express your answer numerically in pound-feet to three significant figures. As shown, a server at a restaurant is carrying a tray that has a glass of water resting on it. The glass and tray exert a force with magnitude F1 = 5.60lb on the server's hand. If l1 = 1.45ft , l2 = 1.00ft , l3 = 0.400ft , ?1 = 165?, and ?2 = 110?, what is the moment of force about the shoulder joint at point A? Assume that moments acting in the counterclockwise direction about point A are positive whereas moments acting in the clockwise direction are negative.

Explanation / Answer

To fnd the moment of force about A, we just need to find the perpendicular distance of line of action of force from point A.

d = L1*cos(180-alpha1) - L2*cos(180-alpha2) - L3

= 1.45 * cos(180-165) - 1 * cos(180 - 110) - 0.4

= 1.4 - 0.342 - 0.4

= 0.658 ft

So, moment acting = 0.658 * 5.6 = 3.685 lb-ft

  

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