Maximum Height of Vertically Thrown Rock

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To determine the rock's velocity after 2.1 seconds of being thrown upwards at 33.4 m/s, the equation V = Vo + at is used, with acceleration due to gravity as -9.8 m/s². The correct calculation yields a final velocity of 54 m/s, but the negative sign for gravity must be applied to get the accurate result. For finding the maximum height of the rock, the equation V² = Vo² + 2a(X - Xo) is recommended. This approach accounts for the upward motion against gravitational pull. Understanding these equations is essential for solving projectile motion problems effectively.
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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+Vot+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.
 
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When going up the pull of the Earth will retard it so put '-9.8'.
 
Thank You! I got the answer right! But what equation would I use to find the maximum height of the rock?
 
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