Solving for Building Height and Time in Horizontal Projectile Motion

[harujina]

Homework Statement

A ball is thrown horizontally from the top of a building and lands 20.0m away from it. If the ball is initially thrown at a velocity of 10.0m/s, how high is the building? How long does it take for the ball to reach the ground?

Homework Equations

dv = Viv * t + 1/2a * t

The Attempt at a Solution

dh (horiz.distance) = 20.0m
Vh = 10.0m/s
Viv (vertical init. velocity) = 0m/s
a = -9.8m/s
dv (vert. distance) = ?
t = ?

I'm confused because I'm missing two of the variables which are needed in the equation that will solve this problem...? (dv and t)

 

[NascentOxygen]

The horizontal velocity of the ball is fixed and constant during the whole time of flight. Knowing this, you can determine the time of flight.

 

[harujina]

Using the same equation as the one stated above? Because that one's giving me a totally wrong answer.

 

[haruspex]

Using the same equation as the one stated above? Because that one's giving me a totally wrong answer.

Yes, the same equation, but of course in the horizontal direction a = 0. pls post your working.