Answer:
(a). D(t) = (√2gh)t - 1/2gt²
(b). D(t) = tk [(√2gh) + g(tk - 2t) / 2]
Explanation:
we would be using the equation of motion to determine the distance D
from the question;
H-boris = h₀ + V₀ (t - tk) - 1/2g(t -tk)²
H-arabella = h₀ + V₀t - 1/2gt²
(a). the vertical displacement is given;
D(t) = H-arabella - H-boris
D(t) = hâ‚€ + Vâ‚€t -1/2gtâ‚‚ - (hâ‚€ + Vâ‚€(t-tk) -1/2g(t-tk)â‚‚)
D(t) = h₀ + V₀t - 1/2gt₂ - h₀ where 0 ∠t ∠tk
this gives D(t) = V₀t -1/2gt²
where V₀ = √2gh
∴ D(t) = (√2gh)t - 1/2gt²
(b). We already know vertical displacement as;
D(t) = H-arabella - H-boris
D(t) = hâ‚€ + Vâ‚€t -1/2gtâ‚‚ - (hâ‚€ + Vâ‚€(t-tk) -1/2g(t-tk)â‚‚)
= V₀tk - 1/2gt² + 1/2g(t -tk)²
 = V₀tk + 1/2gtk² - gttk
 = √2gh tk + 1/2gt² - gttk
this gives D(t) = tk [(√2gh) + g(tk - 2t) / 2]
cheers i hope this helps.