Time at which a projectile reaches a certain height

[enantiomer1]

Homework Statement

Hey, I think I understand this question but there's one or two parts that are really confusing me, the question is:
A major leaguer hits a baseball so that it leaves the bat at a speed of 31.0 m/s and at an angle of 36.1 degrees above the horizontal. You can ignore air resistance.
At what two times is the baseball at a height of 10.0 m above the point at which it left the bat?

Homework Equations

I realize that the equation I should be using is:
y=(v₀sin)*t- 1/2*g*t²

The Attempt at a Solution

so far I've tried various things but I fee like I'm missing something cause I can't figure out how to get t, is there some variabe or function for t that I can substitute in order to get the equation?

 

[Delphi51]

You could do it by trial and error - put in various times and see when y = 10.
Graph the whole thing on a calculator and trace until you find points with y = 10.

When you replace y with 10, you will have a quadratic equation which can be solved in various ways - notably the quadratic formula.

 

[enantiomer1]

that's nice and all, but it isn't going to help me on the test

 

[velocityay]

find out it's maximum height and the time it reaches it. from there you can add or subract time to find when it's 10m high

 

[NBAJam100]

that's nice and all, but it isn't going to help me on the test

Im pretty sure what delphi said WILL help you on the test and is the best way to go about the problem.

you were given a y-function and you know that you are looking for a height of 10m. You know the angle, Vo and g. As delphi said, that gives you a quadratic. You solve the quadratic formula for values of t when the ball is 10 meters high. You'll get two values for that...