(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Hello, after searching the internet I found this very active community and hope you can help me with my problem.

On the Khan Academy website (Which I highly recommend) there are exercises such as Kinematic Equations. I was asked to solve Vi (Initial velocity) so I used the following equation (Screenshot also includes the question and how the answer is worked out by Khan):

See Screenshot https://picasaweb.google.com/lh/photo/nwDuyEjZTsXZd6JbDi7V-tb5egBDP4LQWFyAOijQ15s?feat=directlink" [Broken]

This could have come out as both negative or positive as the answer was a square root, my question is how do I determine which answer is right? With time its obvious that the answer must be positive but with acceleration or Initial velocity I do not see a way (As shown in the screenshot where I entered the answer with the wrong sign).

2. Relevant equations

Relevant equation is demonstrated in the https://picasaweb.google.com/lh/photo/nwDuyEjZTsXZd6JbDi7V-tb5egBDP4LQWFyAOijQ15s?feat=directlink" [Broken].

3. The attempt at a solution

The https://picasaweb.google.com/lh/photo/nwDuyEjZTsXZd6JbDi7V-tb5egBDP4LQWFyAOijQ15s?feat=directlink" [Broken] above shows both the question and my attempt at a solution.

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# Homework Help: Kinematic Equations, solving a quadratic gives two solutions?

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