A bit of a repost, but I have a different question. This is the question given:

If an object is thrown downward at 26 m/s from the top of a building, 102m high, the equation relating to displacement (meters) and time (seconds) is:

$\displaystyle ]s(t) = 1/2 gt^2 + 26t + 102$

Find the time for an object to reach the ground from the top. Use g=-9.81

So I have come up with

$\displaystyle (-26) +/- \sqrt (26)^2 - 4(-4.905)(102) / 2(-4.905)$

Unfortunately I keep getting 2 negative solutions.

I was given this explaination:

The initial velocity is (you are working with s positive upwards) and , so your equation for displacement is:

which I can tell you has exactly one positive root (and in consequence one negative root, but that is not the one you want).

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My question is, how do I figure out I need to use -26t? Am I supposed to look at the given formula and change 26t to a negative number because I am dropping an object?