Results 1 to 2 of 2

Math Help - please help word problem

  1. #1
    billyducky@hotmail.com
    Guest

    please help word problem

    You throw a ball downward with an initial speed of 10 feet per second out of a window to the ground 20 feet below. How long will it take to hit the ground
    Last edited by billyducky@hotmail.com; March 4th 2008 at 08:11 PM. Reason: made mistake
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Aryth's Avatar
    Joined
    Feb 2007
    From
    USA
    Posts
    652
    Thanks
    2
    Awards
    1
    Quote Originally Posted by billyducky@hotmail.com View Post
    You throw a ball downward with an initial speed of 10 feet per second out of a window to the ground 20 feet below. How long will it take to hit the ground
    Well, this is a simple free-fall problem. We have an initial speed and a vertical distance, so, we use our traditional kinematic formulas to solve the problem:

    First, we record what we have:

    \text{Initial Position: 0m}

    \text{Final Position: 20m}

    \text{Initial Velocity: }10\frac{ft}{sec}

    \text{Final Velocity: ?}

    \text{Time: ?}

    \text{Acceleration: }32\frac{ft}{sec^2}

    Now, if there are 2 or less question marks, we can solve the problem, so it looks solvable.

    The next part would be to pick the correct equation, A first step would be to find the final velocity, this equation is perfect for that:

    v_{fy}^2 = v_{iy}^2 + 2a(y_f - y_i)

    Now we plug in what we know:

    v_{fy}^2 = 100 + 64(20)

    v_{fy} = \sqrt{1380}

    v_{fy} = 37.15 \frac{ft}{sec}

    Now, we use what we have now to find the time, this equation is simple and elegant:

    v_{fy} = v_{iy} + a_yt

    37.15 = 10 + 32t

    27.15 = 32t

    0.85 sec = t

    And there you go.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. word problem - the snow plough problem?
    Posted in the Differential Equations Forum
    Replies: 1
    Last Post: October 13th 2011, 02:02 PM
  2. Replies: 3
    Last Post: January 2nd 2011, 09:20 PM
  3. 1 Word problem and 1 function problem
    Posted in the Algebra Forum
    Replies: 8
    Last Post: April 21st 2010, 09:01 AM
  4. Replies: 2
    Last Post: January 10th 2009, 06:49 AM

Search Tags


/mathhelpforum @mathhelpforum