# Projectile - what angle?

Hello All,

I have a question on projectiles, but I am unsure what formula I need to use to calculate the required angle.

A projectile leaves the nozzle at 14 m/s, at what angle should the nozzle be so that it hits the nearest edge at the top of a wall 0.7m high with a horizontal distance oy 19m from the nozzle?

 jeepey Posts: 19, Reputation: 1 New Member #11 Feb 27, 2007, 07:41 AM
Quote:
 I'm bad at this part of math.
your not the only one! Lol
 Capuchin Posts: 5,319, Reputation: 3601 Uber Member #12 Feb 27, 2007, 07:46 AM
Hopefully asterisk will pop his head in, I told him to, he'll hopefully have some time to help right now
 asterisk_man Posts: 476, Reputation: 175 Full Member #13 Feb 27, 2007, 08:21 AM
Somewhat busy right now so don't hold me to this!

$0.7 = \frac{19sin\theta}{cos\theta} - 9.025cos^2\theta$
The real problem is solving for $\theta$...obviously
Sin/cos=tan and
$\cos^2 \theta = \frac {1 + \cos (2\theta ) } 2 \\
\text {so} \\
0.7=19 \tan \theta - 4.5125 - 4.5125 \cos (2\theta) \\
5.2125= 19 \tan \theta - 4.5125 \cos (2\theta)
$

Unfortunately my brain is unable to figure out how you solve for theta at the moment
Numerically I think the answer is:

If I substitute into the first equation I listed then I do get 0.7

Someone else can try to substitute this back into the original equations to see if it really does provide the correct answer. Or i'll try more later if I get a chance.

Sorry I couldn't provide more help. I also dislike trig identities
 jeepey Posts: 19, Reputation: 1 New Member #14 Feb 27, 2007, 10:46 PM
Thanks for the help guys, this problem is more complicated than 1st seems. Some parts of the workings I am struggling to follow, but have helped.
 jeepey Posts: 19, Reputation: 1 New Member #15 Mar 5, 2007, 05:24 AM
Sorry I am re visiting this question

I'm not sure if I'm right, but would the -9.025cos^2 theta not be -9.025cos^-2 theta as its being devided by?
 Capuchin Posts: 5,319, Reputation: 3601 Uber Member #16 Mar 5, 2007, 05:30 AM
I don't think it is being divided by..

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