[tex]k=100 \ N/m \\ \vec{F}_e=40 \ N \\ l_1=13 \ cm \\ k=\frac{\vec{F}_e}{\Delta l} \ \Rightarrow \Delta l=\frac{\vec{F}_e}{k} \\ \Rightarrow \Delta l=\frac{40 \ N}{100 \ N/m} \\ \Rightarrow \boxed{\Delta l=0,4\ m=\bold{40 \ cm}}; \\ \Delta l=l_2-l_1 \\ \Rightarrow l_2=\Delta l+l_1=40 \ cm+13 \ cm \\ \Rightarrow \boxed{l_2=53 \ cm}.[/tex]
