use the equation of motion under gravity
v = u + at Β where v = final velocity , u = initial velocity, t = time and a = acceleration due to gravity. At maximum height v = 0. Also u = 128 ft/s , a = -32 f/s/s and t is to be found. SoΒ
0 = 128 - 32t
32t = 128Β
t = 4 secs Β <--- Β answer to 19a.
19bΒ
v^2 = u^2 + 2as Β where s = distance:-
0 = 128^2 - 2*32*s
s = 128^2 / Β 64 Β = Β 256 feet Β
