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: Leaping Salmon

  1. Jan 24, 2005 #1
    Salmon swimming up a river to their spawning grounds, leap over all sorts of obtacles. The unofficial salmon-altitude record is a 3.56m jump. Assuming that the salmon took off at a 45 degree angle, what was the speed at which it was emerging from the water?

    Xo = 0m
    Yo = 0m
    Y = 3.56m
    a = 9.8m/s^2
    X = ???
    v = ???

    and I thought of using this formula : Y = Yo + VYo(t) + (0.5)(a)(t)^2
    but I couldn't because I dont have t.
    Last edited: Jan 24, 2005
  2. jcsd
  3. Jan 24, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Hint: it's a 45 degree angle, so you should see from a vector diagram that initially v_x = v_y. Calculate the initial vertical velocity required for it to reach a max height of 3.56 metres, and then use that (v0y) to get v0.

    Big Hint...if the fish doesn't go any higher than 3.56 metres, then obviously its final velocity (what you have called v) is zero. So now, you want to find the change in vertical velocity. You know the vertical acceleration. You know the maximum height reached. The two unknowns are therefore v0y and t. If you also use the equation v = v0y +at...then you have two equations and two unknowns. The problem is finished.
    Last edited: Jan 24, 2005
  4. Jan 25, 2005 #3
    here's what i did for this problem:

    (Vy)^2 = (Vyo)^2 - 2g(y - yo)
    0 = (Vyo)^2 - 2(9.8m/s^2)(3.5m-0m)
    Vyo = 8.35m/s

    my answer was incorrect however, I was wondering where I went wrong...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook