Question

Nu știu sa fac varianta 81 , va rog sa mă ajutați

Answer 1

$pt.m:\vec{f}+\vec{N}+\vec{G}=m\vec{a}\\Ox:f=ma\\Oy:N-mg=0\\f=ma=1*\sqrt{3}=\sqrt{3} N=>f=\sqrt{3} N\\Pt.M:\vec{G'}+\vec{N'}+\vec{F}+\vec{f}=M\vec{a}\\Oy:N'-Mg-Fsin\alpha=0\\Ox:Fcos\alpha-f=Ma=>F=\frac{Ma+f}{cos\alpha}=\frac{4*\sqrt{3}+\sqrt{3}}{\frac{\sqrt{3}}{2} } =\frac{10\sqrt{3}}{\sqrt{3}}=10 N=>F=10N$

$N'=Mg+Fsin\alpha=4*10+10*0,5=40+5=45 N=>N'=45 N\\d)r=1 mm=10^{-3} m\\S=\pi r^2=3,14*10^{-6}m^2\\\vec{G'}+\vec{T}=M\vec{a}\\T-Mg=Ma=>T=M(g+a)=4(10+2)=4*12=48 N\\\sigma=\frac{T}{S}=\frac{48}{3,14*10^{-9}}= 15,28*10^{6} N/m^2=>\sigma=15,28*10^{6} N/m^2$