# Find the initial angle.

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1. Oct 4, 2015

### Marcin H

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

Find two elevation angles that will enable a shell, fired from

ground level with a muzzle speed of 800 ft/s, to hit a groundlevel

target 10,000 ft away.

2. Relevant equations
Look at attached picture

3. The attempt at a solution
Look at attached picture

***I get to cos(x)sin(x)=1/4, but I don't think you can solve that for an angle x...

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2. Oct 5, 2015

### Marcin H

***UPDATE***

I got one of the angles, and it checks out with the answer key, but how on earth do I get the angle of 15???

MY WORK:

3. Oct 5, 2015

### Staff: Mentor

You have a mistake in your work. As best as I can tell, your answer is close only due to a coincidence.

One of your equations is $50\sin(\theta) = t$ and the other is $800 \cos(\theta)t = 10000$
Your mistake is in solving for $\sin(\theta)$ in the first equation. It should be $\sin(\theta) = \frac t {50}$.

BTW, please make an effort to post your work here, rather than as an image. Your work is somewhat difficult to read.

4. Oct 5, 2015

### azizlwl

S=ut-½at2. (1)
R=vt. (2)

Just eliminate t, and substitute data in the last equation.