[tex]G=90 \ N \\ \Delta l=8 \ cm=0,08 \ m \\ l_0=9 \ cm=0,09 \ m \\ S=400 \ mm^2=0,000 \ 4 \ m^2 \\ \boxed{E -?} \\ \bold{Rezolvare:} \\ \boxed{E=\frac{\sigma}{\epsilon}} \\ \sigma=\frac{F}{S} \\ F=G=90 \ N \\ \sigma=\frac{90 \ N}{0,000 \ 4 \ m^2}=225 \ 000 \ N/m^2 \\ \epsilon=\frac{\Delta l}{l_0} \\ \epsilon=\frac{0,08 \ m}{0,09 \ m} =0,89 \\ E=\frac{225 \ 000 \ N/m^2}{0,89} \\ \Rightarrow \boxed{E=253 \ 125 \ N/m^2}[/tex]
