Calculating the Velocity and Time of a Freely Falling Rock

[ThiagoG]

Homework Statement

A small rock is thrown vertically upward with a speed of
from the edge of the roof of a 30.0-m-tall building. The
rock doesn’t hit the building on its way back down and lands in the
street below. Air resistance can be neglected. (a) What is the speed
of the rock just before it hits the street? (b) How much time elapses
from when the rock is thrown until it hits the street?

Homework Equations

0=30+18t-4.9t²
Vx=30-9.8t

The Attempt at a Solution

For the time I got 9.8s and for the velocity I got -66.04 m/s. I'm not sure where I went wrong.

 

[Lamebert]

You didn't provide the initial velocity.

 

[ThiagoG]

You didn't provide the initial velocity.

Sorry about that. The initial velocity is 18 m/s.