Answer: (a) 5 s; (b) 50 m/s
Free fall from rest: u = 0, s = h = 125 m, a = g = 10 m/s². (The mass does not affect free fall.)
(a) \(s = ut + \tfrac12 g t^2\): \(125 = 5t^2\), so \(t^2 = 25\) and t = 5 s.
(b) \(v = u + gt = 0 + 10 \times 5 = 50\) m/s.