- #1

realfuzzhead

- 14

- 0

## Homework Statement

This a trajectory problem. A ball is launched from ground level at a unknown angle. ( ∅

_{o}= ? ) at an unknown velocity ( V

_{o}= ? )

The ball travels 20 meters in the x direction and 25 meters up in the y direction. At this point (20,25) the ball hits a wall and a -45 angle below the horizon. Find the initial velocity ( Mag and direction ) and the speed when the ball hits the wall

## Homework Equations

the only equations we have been given are

V

_{yfinal}= V

_{o}( Sin ∅

_{o}) - gt

Δ Y = V

_{o}( Sin ∅

_{o}) - 1/2g (t)^2

ΔX = V

_{o}(cos ∅) (t)

V

_{o}( Cos ∅

_{o}) = Vf(Cos ∅

_{o})

Xmax = (V

_{o}^2 * (Sin 2∅))/ g

## The Attempt at a Solution

I cannot post all my notes. I have finished, and double checked all my other answers on 2 whole trajectory work sheets. But I cannot for the life of me figure out how to find the initial angle as a function of the final angle again the change in distance.

I have even tried switching the whole problem around and shooting at 45° from 25 meters up and I still cannot find a result that works.

I have done probably 10-11 different tries of canceling out different variables (especially Vo and Vf and T) and finding them as products or sums of other variables, but I can never find a way to get the original y velocity or the orignal x velocity.

I do know that when the ball hits the wall the Y velocity is = to the -(x velocity), because tan-1 45° = -1 (-y/x)

I have spent over 2 hours on this problem and I have searched the interwbs for help but I cannot for the life of me figure out how to find the original angle if I know the final angle but don't know either the final or intial x or y velocities. I also don't know the time

I really, really don't like asking for answers to problems because I really like sitting down with a cup of joe and figuring it out for myself and actually learning, but I literally have grown some grey hairs and ruined my weekend over the amount of stress I have experienced over this problem, and I would really really appreciate if someone could answer this one if not give me a HUGE hint