# HELP A question on Kinematics in 2D & 3D?

1. Sep 21, 2008

### Kudo Shinichi

HELP!!! A question on Kinematics in 2D & 3D?

1. The problem statement, all variables and given/known data

A gun is placed at the base of a hill whose slope makes an angle alpha with the horizontal. If the gun is set at an angle theta with the horizontal and has a muzzle velocity Vo, find the distance, measured along the hill, at which the bullet will fall.

3. The attempt at a solution
I know that I need to separate this question in to two equations/ two 1D problems (x-axis and y axis)
Velocity for x = Vo* cos(Θ-α) - g * t * sin(α)
X = Xo + Vo * t * cos(Θ-α) - 0.5 * g * t^2 * sin(α)
Velocity for y = Vo* sin(Θ-α) - g * t * cos(α)
Y = Yo + Vo * t * sin(Θ-α) - 0.5 * g * t^2 * cos(α)

But how can i figure out Vo, Θ, α, Xo, t and Yo

2. Sep 22, 2008

### Kurdt

Staff Emeritus
Re: HELP!!! A question on Kinematics in 2D & 3D?

Seems you've set your axes up so that the x axis runs along the slope. What condition occurs at the point of impact that you can use. That is, what will the value of the y axis be?

3. Sep 22, 2008

### Kudo Shinichi

Re: HELP!!! A question on Kinematics in 2D & 3D?

Do you mean set subsitute one of the variable in y equation from x equation?

4. Sep 22, 2008

### Kurdt

Staff Emeritus
Re: HELP!!! A question on Kinematics in 2D & 3D?

Yes. What will the y position be with the coordinates you chose when the ball lands? You can then get an expression for the flight time and sub it into the x equation which will give you the distance when t is the total flight time.