Results 1 to 2 of 2

Thread: Trajectory question? so confused

  1. #1
    Sep 2010

    Trajectory question? so confused

    The Black Pearl has once again sailed into Port Royal and is firing its guns at the fort. The cannons atop the fort wall have been disabled, but there remains a single cannon at sea level which must defend the town. If the gunner estimates that the ship is 480 meters horizontally from the guns and he knows that the cannon has a muzzle velocity of 87 m/s, at what angle (or angles) should the cannon be aimed so as to hit the Black Pearl? Ignore air resistance, assume and that the cannon and Black Pearl are at the same height above sea level.

    Note: Enter your answers as a single entry, a comma separated list or, if the cannonball cannot hit the ship, enter 'none'.

    The cannon can be fired at ???????? degrees to hit the ship.

    so i have got to the point.
    a (t)= <0 , -9.8>
    v(t)= < 87cos(a) , -9.8t + 87sin(a) >
    p(t)= <$\displaystyle 87cos(a)*t$ , $\displaystyle -4.9t^2 + 87sin(a)t$>

    and we need the point (480,0)

    so $\displaystyle 480 = 87cos(a)*t$
    and $\displaystyle 0 = -4.9t^2 + 87sin(a)t$

    $\displaystyle t= \frac{480}{87cos(a)}$

    therefore$\displaystyle 0 = -4.9[\frac{480}{87cos(a)}]^2 + 87sin(a)[\frac{480}{87cos(a)}]$

    $\displaystyle 0 = \frac{-149.16}{cos(a)^2} + 480tan(a)$

    but i don't know how to simplify it any further to get an angle?
    Last edited by linalg123; May 18th 2013 at 08:26 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Sep 2012

    Re: Trajectory question? so confused

    Hey linalg123.

    Hint: Use the relationship between sec^2(x) and tan^2(x) where sec^2(x) = 1 + tan^2(x) and get everything in terms of tan(x) and tan^2(x) and solve for x.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. On the trajectory of the planet
    Posted in the Differential Equations Forum
    Replies: 1
    Last Post: Oct 16th 2011, 08:03 PM
  2. Differential arc of a trajectory
    Posted in the Calculus Forum
    Replies: 0
    Last Post: Mar 13th 2010, 12:03 PM
  3. Replies: 2
    Last Post: Jan 10th 2010, 08:45 AM
  4. trajectory eq.
    Posted in the Calculus Forum
    Replies: 3
    Last Post: Nov 21st 2009, 12:38 PM
  5. [SOLVED] trajectory flight
    Posted in the Calculus Forum
    Replies: 1
    Last Post: Oct 21st 2006, 01:57 PM

Search Tags

/mathhelpforum @mathhelpforum