Help With Physics Question

but that gives, 0.36N resultant force of the ball, but not the average air resistance

a)

Use:

$v^2=u^2+2as$ (where u=0)

therefore...

$v=\sqrt{2as}=16 \mathrm{ms}^{-1}$

b)

v now equals 8ms^-1 so use the same formula to find a (this is assuming that the ball is under constant acceleration throughout its fall)

$a=\frac{v^2-u^2}{2s}=2.5 \mathrm{ms}^{-1}$ (where u=0)

now using:

$\sum F=ma$ where the total force on the ball is the vector sum of its weight (mg) and air resistance (Fr)

this gives...

$mg-F_r=ma$
$F_r=m(g-a)=1.06\mathrm{N}$

(I think...?)