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Homework Help: Intro Physics projectile problem: Archer fish and grasshopper

  1. Nov 11, 2016 #1

    I uploaded an image of the problem, it seems to be fairly straight forward. However, my textbook indicates the answer as being 6 m/s, I am consistently getting 3 m/s. Any help would be appreciated!!

    Because there is no air resistance, the horizontal velocity is constant.

    We can set the Vo equal to zero, find the required speed to achieve .45m vertically.
    We find Viy=2.97m/s
    2.97/9.81=.3 seconds
    Horizontal speed (distance over time)- constant speed
    .25/.3=.833 m/s

    I know that the height and length indicated in the problem yield a angle of 61 degrees, however, this information still does not yield the correct answer.

    Attached Files:

  2. jcsd
  3. Nov 11, 2016 #2
    On what basis did you set vo equal to zero?
  4. Nov 11, 2016 #3
    You only need to calculate the speed to achieve 0.45m vertically, therefore it would be equivalent to the final speed of an object falling 0.45 meters vertically. Again, no air resistance.
  5. Nov 11, 2016 #4
    The velocity of the spit is not zero when it hits the bird. So neither the initial velocity nor the final velocity of the spit is zero.
  6. Nov 11, 2016 #5
    There remains a constant x/horizontal component of velocity, the y vertical component of velocity can be zero at the point which the spit hits the object. Potentially, the y component of velocity could be nonzero at the top, however without any further information given, you can only assume the final y component of velocity is zero at the top.
  7. Nov 11, 2016 #6


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    You haven't used the given angle of projection in any of your calculations.
  8. Nov 11, 2016 #7
    wow, I really appreciate that.. No idea why I decided to overlook the angle, got 6 m/s. Sorry for bothering you guys. Thank you!!!!!!!
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