At which times will the ball be at a height of 15 meters?

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To determine when the ball reaches a height of 15 meters, the equation D = ViT + ½at² is appropriate, where Vi is the initial velocity of +20 m/sec and a is the acceleration due to gravity, -10 m/sec². The problem requires solving for time using the quadratic formula after substituting D with 15 meters. The correct approach involves rearranging the equation to isolate time and applying the quadratic formula. The discussion confirms that the method of using the quadratic formula is valid for this scenario. Ultimately, the solution will yield the specific times when the ball reaches the desired height.
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Homework Statement



I am in high school physics. This is my problem that I've been trying to work on: A ball is thrown straight upward with a velocity of +20m/sec on a planet where the acceleration due to gravity is -10m/sec². Find the times at which the ball will be at a height of 15 meters.

Homework Equations


Ok, so I started with this equation: D=ViT+½at². I'm not sure if it's the correct one to use, but I'm pretty sure it is...I think I will need to use the quadratic forumla: x= -b+-b²-4ac (square root)/2a. Sorry, I don't know how to make a square root symbol or any of the other signs?!?

The Attempt at a Solution



Now, the problem calls for time, so I must need to solve for it. Next, I got this as the possible equation to utilize when it's solved for time: t-v+- v²+f(1/2a)d (square root) / 2(1/2a)
So far, does everything seem to be right, now all I need to do is "plug and chug?" :) Thanks
-Greg
 
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Just take you equation for D and use the quadratic formula (or some other method) to solve for t when D = 15m. (Note that at t = 0, D = 0)
 
S=ut + 1/2 at^2
it should be used in a straight line motion and uniform acceleration.
 
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