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HW 7 Prob 3_8

# HW 7 Prob 3_8 - (a(b(C a «Mamas-E PROBLEM 3.8 It is known...

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Unformatted text preview: (a) (b) (C) a «Mamas-E PROBLEM 3.8 It is known that a vertical force of 200 lb is required to remove the nail at C from the board. As the nail ﬁrst starts moving, determine (a) the moment about B of the force exerted on the nail, (b) the magnitude of the force P that creates the same moment about B if a =10°, (c) the smallest force P that creates the same moment about B. We have MB = rC,BFN = (4 in.)(200 1b) = 800 lb - in. or MB =8001b-in.)4 By definition M B = 7A,BP sin 9 6=lO°+ (180°~ 70°) =120° Then 800 1b - in. = (18 in.) x Psin120° or P=51.3 lb 4 For P to be minimum, it must be perpendicular to the line joining Points A and B. Thus, P must be directed as shown. Thus M B = dem d = rA/B or 800 lb - in. = (18 in.)Pmin or 13min =44.41b i"min =44.4 1171.200 4 ...
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