Page 32 - 機械群機械力學升學寶典
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ዚɢኪ
ۆ R x = F + F = F + F cosθ
2x
2
1
1
cR y = F = F sinθ
2y
2
2
c R = ( R ) 2 + ( R )
y
x
cc= (F + F 2 cos ) + (F 2 sin)
θ
θ
2
2
1
cc= F + 2 F F cosθ + F cos θ + F sin θ
2
2
2
2
2
2
1
12
2
c c= F + F + 2 FF cosθ
2
2
2
12
1
2
2
c cï sin θ + cos θ = 1
F 2 y F sin θ
tanφ = ⇒ φ = tan −1 2
F + F F + F cos θ
1 2x 1 2
類題
2. ν̛ྡהͪdɚᓃɢ F = 70NdF = 40 2 Nd F =40√2 N
2
2
1
ɚɢѰԉމ 135°d༊ӋՉΥɢٙɽʃމ Ni
135º
˙Σ φ = f
F 1 =70N
精選範例 7 同步練習 7
νɨྡהͪdR = 35N މɚᓃɢ F ၾ νɨྡהͪʘɚɢdՉѰԉމ 60°dΥɢ
1
F ٙΥɢdՉʕ F = 15NdF ၾ F ٙѰ R = 10 3 Nd߰ F = 10Ndۆ F ഃε
1
1
2
2
2
1
ԉމ 60°d༊Ӌ F ٙɽʃމОk ˇ N k
2
F 2 F 2
R R
60º
60º F 1 F 1
༆ ï R = F + F + 2 FF cosθ ഈ
2
2
12
1
2
×
ð 35 = 15 + F 2 + 215×F ×cos 60°
2
2 2
2
c1225 = 225+ F + 15F
2
2
2
cF + 15F – 1000 = 0
2
2
c(F + 40)(F – 25)=0
2
2
cF = –40ʔΥdF = 25N
2
2
22
BD111_CH02.indd 22 23/7/2021 14:57:01