Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Need help solving this

  1. Jan 15, 2008 #1

    Can somebody please help me solve this through completing the square?

    A football player attempts a field goal by kicking the football. The ball follows the path modelled by the equation h=-4.9^2+10t+3, where h is the height of the ball above the ground in metres, and t is the time since the ball was kicked in seconds.

    a) Describe the path of the ball.
    b) After how many seconds does the ball reach the ground?
    c) The ball must clear the uprights for the field goal to count. The uprights are approximately 5m high. How long does the ball stay above 5 m in height?
  2. jcsd
  3. Jan 15, 2008 #2

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Must you do it by completing the square? Why not use the quadratic formula?
  4. Jan 15, 2008 #3
    We should have a mod roll call.
  5. Jan 15, 2008 #4
    I haven't learnt it yet.
  6. Jan 15, 2008 #5

    Gib Z

    User Avatar
    Homework Helper

    Why not prove it then =] ? Completet the square on the general quadratic form [itex]ax^2 + bx + c[/itex], where a, b and c are real constants.
  7. Jan 16, 2008 #6
    which bit are you stuck on exactly?

    for a), its kind of you know it or you dont.

    for b), when the ball hits the ground, you know its height is what?

    from there you can simply solve the quadratric using the quadratic formula (be useful if you can derive it, but just search google if you cant be bothered).

    for c), same sorta method as b), just use a dif value for height.

    need any more help?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook