Kangaroos are very efficient at hopping; they can hop for miles without fatigue. Their legs have very long tendons that act like springs: they stretch and relax on each hop, storing and releasing elastic energy. A kangaroo might have a mass of m=25 kg and two tendons (one in each leg) that are 30 cm long. The effective spring constant of a kangaroo tendon is about K= 4 x 10⁵ N/m.
a) When fully stretched, the tendons increase in length by 2.4 cm. How much elastic energy is stored in tow fully-stretched tendons?
b) Consider a kangaroo at rest whose tendons are fully stretched (storing energy as describe in part a). If all of that elastic energy propels the kangaroo straight up, and the kangaroo