Notam:
F1=35N; L1=5cm; F2=7N; L2=?; F3=63N; L3=?; F4=?; L4=6cm.
Din expresia legii lui Hook:
F1=k×L1
Avem k=F1/L1
Apoi
F2=k×L2; Inlocuim pe k obtinut mai sus:
F2=F1×L2/L1
De unde:
L2=F2×L1/F1
L2=7×5/35=7/7=1cm
L3=F2×L1/F1; L3=63×5/35=9×5/5=9cm
F4=k×L4; k=F1/L1 ⇒F4=(F1/L1)×L4 Sau:
F4=F1×L4/L1
F4=35×6/5=7×6=42N