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Find the initial angle.

  1. Oct 4, 2015 #1
    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...

    Attached Files:

  2. jcsd
  3. Oct 5, 2015 #2

    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:
    New Doc 2Page 1.jpg
    ANSWER KEY.png
  4. Oct 5, 2015 #3


    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.
  5. Oct 5, 2015 #4
    S=ut-½at2. (1)
    R=vt. (2)

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