# Homework Help: Projectile motion (am I on drugs?)

1. Jan 26, 2008

[SOLVED] Projectile motion (am I on drugs?)

1. The problem statement, all variables and given/known data
I can't believe how much time I have spent on this.

2. Relevant equations
Constant acceleration

3. The attempt at a solution
Here is the data I am using to solve for
$V_a$
$x_0=0$,
$x_f=30$,
$y_0=7$,
$y_f=10$,
$a_y=-g=-32.2$,
$V_{0y}=V_a\sin30$,
$V_{0x}=V_a\cos30$

From x direction:
$$\Delta X=V_{0x}t\Rightarrow t=\frac{30}{V_a\cos30}$$

From y direction:
$$\Delta Y=V_{oy}+.5a_yt^2$$
$$\Rightarrow 3= V_a\sin30*(\frac{30}{V_a\cos30})-16.1[\frac{30}{V_a\cos30}]^2$$

$$\Rightarrow 3=30\tan30-16.1*(\frac{40}{V_a})^2$$

Which gets me a negative under the radical!

2. Jan 26, 2008

seriously I am about to lose it. i have been over this like ten times!

3. Jan 26, 2008

### belliott4488

Where's the negative under the radical? 40 and $$V_a$$ are both positive, right? ...

4. Jan 26, 2008

### belliott4488

How'd you get that "40" under the radical, anyway?? I get 34.64 ...

5. Jan 26, 2008

Oh wow. I better look into that drugs thing. The solution is 36.7 but I am getting 42.2. But then again, I'm on drugs. So let me check again.

Thanks B.

6. Jan 26, 2008