How Long Will the Volleyball Be in the Air?

[MIA6]

Homework Statement

Jason hits a volleyball so that it moves with an initial velocity of 6.0 m/s straight upward. If the volleyball starts from 2.0 m above the floor, how long will it be in the air before it strikes the floor?

Homework Equations

y=-2.0m,Vi=+6.0 m/s a=-9.81m/s^2
vf^2=vi^2+2ay. then just put the numbers in it.

The Attempt at a Solution

I don't understand why the displacement here is -2.0m? I don't think it can be used in solving the problem because 2.0m is not the distance that the ball traveled, but just 2.0m above the floor? What's the significance of it?

 

[bel]

The displacement is -2.oo m because that's the distance it ended up at from the starting point. If you think about the displacement time curve, it's a parabola, so if you read across the graph for a displacement of -2.oom, you have two time values, one of them has to be rejected to give the right answer.