Solving for the final velocity of an object thrown off of a Martian Volcano

[garcia1]

The tallest volcano in the solar system is the
19 km tall Martian volcano, Olympus Mons.
An astronaut drops a ball off the rim of the
crater and that the free fall acceleration of the
ball remains constant throughout the ball’s
19 km fall at a value of 4 m/s2. (We assume
that the crater is as deep as the volcano is tall,
which is not usually the case in nature.)
Find the time for the ball to reach the crater
floor.
Answer in units of s.

Find the magnitude of the velocity with which
the ball hits the crater floor.
Answer in units of m/s.

Homework Equations

Vf = Vo +at

The Attempt at a Solution

I simply plugged in values from the first problem's answer, 97.468s, along with the given acceleration and implied initial velocity to make:

Vf = (-4m/s)(97.468s) = -389.872 m/s

This was wrong though, so I'm wondering where I screwed up along the way.

 

[Quinzio]

The solution is correct.

 

[SteamKing]

The problem asks how long it takes for an object to fall 19 km on Mars. Your equation displayed deals only with calculation of velocities. Use the right equation, get the right answer.

 

[SteamKing]

Disregard my last post.

 

[gneill]

The question asks for the magnitude of the velocity. Magnitudes are positive values...