What is the formula for determining how long objects take to fall from a height?

Question

Balls dropped from 54 meters.  How long  to hit the ground?  How fast were the balls going just before they hit the ground?

Answer 1

since you are in meters with an initial velocity of 0 m/sec then the equation is

h(t)=-9.8t^2 + 54  

then how long to hit ground:  h=0 on the ground so -9.8t^2 + 54 = 0

-9.8t^2 = -54

t^2 = 5.51

t = 2.35 seconds (note, even though it is t^2 you don't consider -2.35 also since time cannot be negative)

how fast were they going?  9.8 m/s^2 (2.35 seconds) = 23.03 m/sec downward

Answer 2

the formula is h= -16t squared + vt (initial velocity)+ a number

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