How Long Does It Take for a Marble to Hit the Floor After Rolling Off a Table?

[bigk2331]

Homework Statement

A marble, rolling with speed 20cm/s, rolls off the edge of a table that is 80 cm high. (a) How long does it take to drop to the floor? (b) How far, horizontally, from the table edge does the marble strike the floor?

Homework Equations

y = y0 + vy0t - (1/2)gt2

The Attempt at a Solution

Well I know that

Vx0 = 20cm/s
Vyo = 0
Xo = 0
Yo = 80cm

I've already plugged in what I know for this equation:

y= 80cm + 0 -(1/2)(9.81m/s)t^2

right now I am solving for (a) and I need to know in what order should I perform these order of operations so I get the right answer.

 

[kuruman]

What is y when the marble hits the floor? Also don't forget to convert 80 cm to meters.