A pogo stick is modeled as a massless spring of spring constant k attached to the bottom of a block of mass m. The pogo stick is dropped with the spring pointing downward and hits the ground with speed v. At the moment of the collision, the free end of the spring sticks permanently to the ground. During the subsequent oscillations, the maximum speed of the block is
Answer Choices
A. v
B. v+2 m g^{2} / k v
C. v+m g^{2} / k v
D. \sqrt{v^{2}+2 m g^{2} / k}
E. \sqrt{v^{2}+m g^{2} / k}
