Question

Problem 4.60 The A-frame is being hoisted into an upright position by the vertical force of 78 lb (Figure 1) - Part A Determine the moment of this force about the yaxis when the frame is in the position shown Express your answer to three significant figures and include the appropriate units. THA RO? M, Value Units Submit Request Answ Figure 10t1 Provide Feedback

Answer 1

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solution) y Find the position vector along AC wort X y'aris VAC = -1600815') î +679 +65in 15°)ť SAC = - 51795 î +39 +11553 Ř → Oblein the unit vector along y-asis as below; | CA - -Sn30')) + (C6530 5 My = -0.5ô+ 0.8669 - Express the force vector in the cartesian vector form; F = FR = 78 -> calculate the Moment of the force about y asis, My = Uy, (JAC XF) My =(-0.55+08661)./65.1951 +33+)5538) x768] 7:5.795ả +39 +11553R)x 78À = -5.495 3 1:553 lo o 78

7 (78x3 -0 -J (-5,795 878 -0) + ²lo) = 234 î+ 452001 60.5 +0.8667) · ( 234 +452°015) M = -1179 + 391.44066 My = 274.441 lb ft o find the position vector alony AB wist to x'y' axis. 2880 DAR = (3 Sin30_60081500830) i + (300x30'+6C0815'5in 30) + (65in159) VAB = -3.52î +5.59 +11553| obtain the unit vector along y-axis ; y = (sin 30 )i + (C0830) ]

My = 0.5h +0.866 o boxee vector at C in the cantesion vector form; F = FÅ = 70 . calculate the moment of the force about y-axi; My' = Uys . (NAB XF) M'=(054+0.849)/1-3:52145:39 +15SR) (98)] 10.5 My = 22,52 To 0.866 515 @ 1 11553 . 78 / - M = 0 5 5.5x28 - - 04 ( 352x28) ] 214.5 + 237.769 Myl = 452269 lb-ft /