please help with physics!

Posted on 2015-08-18 11:39:00 in Physics by KYLE

Ok so this is the problem, I know how to do it as it's just a projectile motion problem, but what I'm having trouble with is the quadratic equation as I'm getting two positive values so which one do I use?
So for the y - direction I used d=v0t+1/2at^2 where d = -9 a = -9.81 v0 = -10

so we have t = -10+/-sqrt(100+2(-9.81)(-9))/(9.81)

Here we get two positive values 0.676s and 2.71s so which exactly one do I use, is there a rule of thumb?

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