[tex]\text{a) Principiul al II-lea al mecanicii (acrobatul e in echilibru): }\overrightarrow{F_e}+\overrightarrow{G}=\overrightarrow{0}\qquad(1)\\\text{b) Proiectam ecuatia $(1)$ pe Oy: } F_e-G=0 \implies F_e=G\\\text{Dar, }F_e=k\cdot\Delta l \implies k\cdot\Delta l=G \implies\\\\ k=\frac{G}{\Delta l}=\frac{mg}{\Delta l}=\frac{72\,kg\cdot10\,m/s^2}{3\,m}=240\,N[/tex]
