Find initial velocity only need hint

[itunescape]

Homework Statement

home run hit and baseball just clears the top of the bleachers.
@= 35 degrees
bleacher height = 21 meters
distance from bleachers to home plate = 130 meters

neglect air resistance

find initial velocity and time of flight

Homework Equations

x comp:
x= vcos@ t + at^2/2
y comp
y= vsin@ t + at^2/2
vf^2= vi^2 + 2a(delta x)

The Attempt at a Solution

The thing is, in order to solve for velocity itd help to know the time and to solve for time itd help to know the velocity. So i thought i'd use vf^2= vi^2 + 2a(delta x) since it doesn't have time in the equation. I got
0= (vi cos 35)^2 + 2(9.8) (130)
i keep getting a negative inside the square root and I am stuck.
I just need a hint into the right direction, am i approaching this problem incorrectly?

 

[Mindscrape]

Careful now, you wouldn't have an acceleration in the x direction. Also, do you really think the final velocity would be zero? You really need to know what the equations mean and how vectors work. Remember, you have to do it component wise.

So here's what you know: the distance in the y direction the ball travels, and the distance in the x direction that the ball travels. Two equations and two unknowns.

 

[Moetasim]

It seems like you are on the right track. However, when using the equation vf^2= vi^2 + 2a(delta x), keep in mind that the initial velocity (vi) is what you are trying to solve for. So, you would rearrange the equation to solve for vi and then plug in the given values for delta x and acceleration. Also, make sure to use the correct sign for acceleration (since it is in the opposite direction of the initial velocity).

Another hint is to think about the motion of the baseball in terms of its x and y components separately. In the x direction, the ball is moving at a constant velocity (since air resistance is neglected) and in the y direction, the ball is experiencing constant acceleration due to gravity. You can use the given information about the angle and the height of the bleachers to find the initial velocity in the y direction, and then use that in conjunction with the x-direction velocity to find the overall initial velocity.

Hope this helps!