Trouble with mechanical physics

[fixixisfunmf]

A 70 kg trampoline artist jumps vertically upward from the top of a platform with a speed of 4.5 m/s. (Ignore small changes in gravitational potential energy.

(a) How fast is he going as he lands on the trampoline, 3.0 m below?
m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 5.2 multiplied by 104 N/m, how far does he depress it?
m

I think i have to use kinematics but I don't really know how to execute it

A 1400 kg sports car accelerates from rest to 80 km/h in 7.4 s. What is the average power delivered by the engine?
I put 112000 W but it is wrong and I don't know what to do to get it write

please help me with one or both of these that would be great

 

[fluidistic]

For part (a), think about the conservation of mechanical energy. ($$E=\frac{mv^2}{2}+mgh$$).

For part (b), use Hook's law. (Check out wikipedia or google it).