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Homework Help: Projectile Motion Question

  1. Oct 13, 2008 #1
    1. The problem statement, all variables and given/known data

    An insect is resting above the water level on a leaf, a horizontal 0.600 m away from a fish. The fish shoots water into the air above the surface of the water at a 60 degree angle, with an initial velocity of 3.01 m/s.

    Assume the fish shoots the water into the air at water level, and that the water hits the insect.

    At what height is the leaf above water level?

    2. Relevant equations
    v = vi + at
    v= d/t
    x = vi(t) + 0.5a(t^2)

    3. The attempt at a solution
    First I tried to find out how much time it would take the water to travel in the horizontal direction.

    Initial velocity in horizontal direction: cos60*3.01= 1.505 m/s
    With zero acceleration, the time it would take to travel 0.600 m would be:
    t=0.600/1.505=0.398 s

    Then, I tried to figure out where the water would be at 0.398 seconds vertically.
    Its initial velocity is sin60*3.01 = 2.60 m/s
    2.60(0.398)+(0.5)(-9.81)(0.398^2)= 0.259 m

    I must be doing something wrong because the program says I have the wrong answer. I have no idea where the problem is, though... any ideas?
  2. jcsd
  3. Oct 13, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    You have rounded at the intermediate steps, which has induced errors in your final answer. Try to use the exact values of the intermediate steps by either storing them in your calculator, or writing down the full calculator display.
  4. Oct 13, 2008 #3
    Thanks, I think that solves the problem.
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