Maximum Height of Vertically Thrown Rock

[jojo711]

Homework Statement

Brad tosses a rock straight up at 33.4 m/s. What is the rock's velocity after 2.1 seconds?

Homework Equations

V=Vo+at
X=Xo+volt+1/2at^2
V^2=Vo2+2a(X-Xo)

The Attempt at a Solution

I used the first equation. V=33.4m/s+9.8(2.1) 9.8 being the acceleration due to gravity. The hint says 'Final velocity equals the initial velocity plus the product of acceleration due to gravity (g) multiplied by the time.' I kept getting the incorrect answer of 54m/s.

 

[grzz]

When going up the pull of the Earth will retard it so put '-9.8'.

 

[jojo711]

Thank You! I got the answer right! But what equation would I use to find the maximum height of the rock?