Find initial velocity only need hint

AI Thread Summary
To find the initial velocity of a baseball that just clears a 21-meter bleacher from a distance of 130 meters at a 35-degree angle, it's essential to use the correct equations of motion. The discussion highlights the challenge of solving for both initial velocity and time of flight simultaneously, as they are interdependent. The participant attempted to use the equation vf^2 = vi^2 + 2a(delta x) but encountered a negative value under the square root, indicating a misapplication of the equation. It is emphasized that acceleration only acts in the vertical direction, and the final velocity should not be assumed to be zero. The solution requires breaking down the problem into x and y components to correctly apply the equations of motion.
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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?
 
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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.
 
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