(a) The glasses are a height y above the ground at time t according to
y = 225 m - 1/2 g t²
where g = 9.80 m/s² is the magnitude of the acceleration due to gravity. They reach the ground when y = 0 :
0 = 225 m - 1/2 g t²
t² = (450 m) / g
t ≈ 6.78 s
(b) The glasses have a velocity v of
v = - g t
so that at the time they hit the ground, they do so with a velocity of
v = - g (6.78 s)
v ≈ 66.4 m/s
