[tex]\tt Se~da:\\ \\
G=1200N\\ \\
l=3m\\ \\
d=2,7m\\ \\
\mu=0,1\\ \\
a)N=?N\\ \\
b)F=?N\\ \\
c)L_{fr}=?J\\ \\
d)t=10s;~P=?W\\ \\
e)\eta=?\\ \\ \\
Rezolvare: \\ \\
Clar~lucru~ca~platforma~reprezinta~un~plan~inclinat.\\
Deci~conform~teoremei~lui~Pitagora~aflam~inaltimea~planului:\\ \\
h=\sqrt{l^{2}-d^{2}};~h=\sqrt{3^{2}-2,7^{2}}\approx 1,3m\\ \\ \\[/tex]
[tex]a)N=G_{y}\\ \\
N=G \times \cos \alpha \\ \\
N=G \times \frac{d}{l}\\ \\ \\
b)F=G_{x}+F_{fr}\\ \\
F=G \times \frac{h}{l}+\mu \times N\\ \\ \\
c)L_{fr}=-F_{fr} \times l \\ \\
L_{fr}=-\mu \times N \times l \\ \\ \\
d)P=F\times v \\ \\
P=F \times \frac{l}{t}\\ \\ \\
e)\eta=\frac{L_{u}}{L_{c}}\\ \\
\eta=\frac{G \times h }{F \times l}\\ \\ \\
[/tex]
[tex]Calcule:\\ \\
a)N=1200 \times \frac{2,7}{3}=1080N\\ \\
b)F=1200 \times \frac{1,3}{3}+0,1 \times 1080=628N\\ \\
c)L_{fr}=-0,1 \times 1080 \times 3 =-324J\\ \\
d)P=628 \times \frac{3}{10}=188,4W\\ \\
e)\eta=\frac{1200 \times 1,3 }{628 \times 3}\approx 0,828\\ \\ [/tex]
