When playing a game, a 45 kg boy jumps vertically upward from the top of a wardrobe with a speed of 5.5 m/s. (Ignore small changes in gravitational potential energy). Then he falls onto a mattress.
(a) How fast is he going as he lands on the mattress, 3 m below? m/s
(b) If the mattress behaves like a spring with spring constant 4 104 N/m, how far does he depress the mattress? m