1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Projectile motion of a diver

  1. Apr 18, 2008 #1
    1. The problem statement, all variables and given/known data

    A diver leaves a 3-m board on a trajectory that takes her 2.5 m above the board, and the into the water a horizontal distance of 2.8 m from the end of the board. At what speed and angle did she leave the board? Book answer is 7.2 m/s at 77 degrees to the horizontal.

    2. Relevant equations

    y= y0 + vy0t - 1/2gt^2

    y = x tan theta0 - g/2v0^2 cos^2 theta0*x^2

    3. The attempt at a solution

    If the origin is at water level, then at the top of the dive vy0 = 0,and 1/2/gt^2 = 5.5 m. Therefore, t = 1.06 s. I still have two unknowns, v0 and theta, but only one equation.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 18, 2008 #2

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Assuming the t = 1.06 s is right (and I haven't checked too closely), then that means it took her that long to travel a horizontal distance of 2.8 m. So, what was her horizontal velocity?

    The time value may actually be wrong, because I think you must use the difference between her final height and her initial height to determine t. (Can you see why it doesn't make sense otherwise? She didn't actually go UP 5.5 m).

    Also, if her vertical velocity went from whatever it was initially to zero at the top of the dive in that amount of time, what was her initial vertical velocity? (hint: vy = vy0 - gt)

    If you know both the initial vertical and initial horizontal velocity, then you know the angle.
     
  4. Apr 18, 2008 #3
    I do not know the initial velocity. That is what I am trying to solve for, as wll as the angle.
     
  5. Apr 18, 2008 #4

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I know that. That's why I was trying to explain to you how to find them. Maybe you should read what I said more closely.
     
  6. Apr 18, 2008 #5
    I am still having trouble. If y0 is at the water, then the total y dispacement is 5.5 m--2.5 m above the board and 3 m below the board. I still cant come up with 7.2 m/s for v0 no matter how I solve for it.
     
  7. Apr 18, 2008 #6
    Okay, I finally got it. Thanks
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Projectile motion of a diver
  1. Diver Proj. Motion (Replies: 3)

Loading...