[填空题]
A 65-kg trampoline artist jumpsuqt,2fe(4e-* yz- u e 4xehs fzqygh5; vertically u ef mitt8pd1+/x-g;zrpward from the top of a platform with a d+t8-g;t1mi ezr /fpxspeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$ m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ = m