Question

An object is dropped from a platform 100 feet high. Ignoring wind resistance, what will its speed be when it reaches the ground?

_____ ft/s

Answer 1

the answer to the question is 2.5

Answer 2

if we assume the origin is at the dropping point and the object is merely dropped and not thrown up or down then y0 = 0 and v0 = 0. The equation reduces to

y = 0 + 0t + ½gt²
y = ½gt²

t = √(2y/g)

in the ft - lb - s system

y = -100 ft
g = -32.2 ft / s²

t = √(2y/g)
t = √(2(-100) / (-32.2))
t = 2.5 s