# Homework Help: Finding t for projectile motion without initial velocity

1. Oct 16, 2011

### vsindorf

1. The problem statement, all variables and given/known data
An arrow is shot at an angle of θ=45* above the horizontal. The arrow hits a tree a horizontal distance D=220m away, at the same height above the ground as it was shot.
Use g=9.8m/s^2 for the magnitude of the acceleration due to gravity.

Find t, the time that the arrow spends in the air (in seconds).

2. Relevant equations
1) (Vy)i = Vi*sinθ
2) (Vx)i = Vi*cosθ
3) Xf = Xi + (Vx)i*Δt
4) Yf = Yi + (Vy)i*Δt - 1/2g(Δt)^2

3. The attempt at a solution
I have tried going about reconfiguring equations in several different ways to come up with an equation that will give me t, but I'm not doing so well. I don't understand how I can come up with this answer without any information about time, acceleration, or velocity.

any help you can give me to steer me in the right direction for finding components of initial velocity or Δt would be extremely helpful.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Oct 16, 2011