m = 7kg
m (∡α) = 30°
F = 103 N
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a) Gp, Gn = ?
b) reprezentare grafică
c) Ff = ?
d) [tex]\displaystyle{ \mu = \ ? }[/tex]
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a)
Gp = G × sin α = mg × sin α
Gp = 7 × 10 × sin 30°
Gp = 70 × 1/2
Gp = 35 N
Gn = G × cos α = mg × cos α
Gn = 7 × 10 × cos 30°
Gn = 70 × √3/2
Gn ≅ 35 × 1,73
Gn ≅ 60,55 N
b) vezi imaginea atasata
c)
PII (m): Ox: F + Gp - Ff = 0
F + Gp = Ff
Ff = 103 + 35
Ff = 138 N
d)
PII (m): Oy: N - Gn = 0 ⇒ N = Gn
N = 60,55 N
Ff = [tex]\displaystyle{ \mu }[/tex] × N ⇒ [tex]\displaystyle{ \mu }[/tex] = Ff/N
[tex]\displaystyle{ \mu = 138 : 60,55 }[/tex]
[tex]\displaystyle{ \mu = 2,27 }[/tex]
Fals. Coeficientul de frecare este intotdeuna subunitar ⇒ datele problemei sunt gresite.
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Matei.
