Aprojectile is launched upward from ground level with an intentional speed of 98 m/s. how high will it go? when will it return to the ground?

Check the picture below.

now, keeping in mind that gravity will pull the projectile down, and that'd be 9.8 m/s², that gets halfed for the initial velocity equation, so 9.8/2 or 4.9 m/s².



how high will it go?  well, notice in the picture, it'll go as high as its vertex,



when will it return to the ground?  well, notice the picture, when y = 0.



so after "t" seconds it comes back down.

notice is 0 at two points, at t=0 or 0 seconds, because it just took off the ground, and again the second time, when it comes back down.