Question

physics ................

Answer 1

see this solution it is based on motion in 1 d

Answer 2

$s = ut + \frac{1}{2} a {t}^{2} \\ 0 = 4u - 5 \times 16 \\ u = 20$
now
${v}^{2} = {u}^{2} + 2as \\ 0 = 400 - 2 \times 10 \times s \\ s = 20$
max height=20 m
now
s=ut+1/2at^2
s=60-45
s=15