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1 如圖所示,試求四力之合力距A點之距離為若干?
A 3m
B 4m
C 5m
D 6m

合力R=∑Fy

=20+30+10-15=45(N,↓)

∑MA=20×0+30×4+10×9-15×2

=120+90-30=180(N.m,順時針)

∑MA=45.X=180

X=4(m)