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Find vertical distance of missed shot

  1. Mar 15, 2017 #1
    1. The problem statement, all variables and given/known data
    A hunter is aiming a blowgun directly at a bird on a tree branch 4.0 m above the blowgun and 10 m away. If the speed of the dart is 25.0 m/s and the bird stays in place, by what vertical distance will the dart miss the bird?

    2. Relevant equations
    s= ut + 0.5at2

    3. The attempt at a solution
    the angle(b) of the blowgun is
    tanb=4/10 b =21.8

    in x direction
    u = 25cosb =23.2
    a=0
    s=10
    so t=10/23.2 = 0.43

    in y direction
    t = 0.43
    a=-9.8
    u= 25sinb = 9.28

    s=ut +0.5at2
    s= 3.086

    vertical distance of miss = 4 - 3.086 = 0.91

    My answer is marked wrong but what is wrong with it?
     
  2. jcsd
  3. Mar 15, 2017 #2
    I couldn't see anything wrong with it unless I made the same mistake you did.
     
  4. Mar 15, 2017 #3

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Your work looks correct. Was a diagram included with the problem? The phrase "10 m away" could mean that the straight line distance between the hunter and the bird is 10 m.
     
  5. Mar 15, 2017 #4
    Good point.
     
  6. Mar 15, 2017 #5
    ah ..ofcourse. Thank you:wink:
     
  7. Mar 19, 2017 #6
    actually guys, I tried it again and the answer I'm getting is still marked wrong.

    the angle(b) of the blowgun is
    sinb=4/10 b =23.58

    in x direction
    u = 25cosb =22.9
    a=0
    s=10cosb =9.17
    so t=9.17/22.9 = 0.4

    in y direction
    t = 0.40
    a=-9.8
    u= 25sinb = 10

    s=ut +0.5at^2
    s= 3.216

    vertical distance of miss = 4 - 3.216 = 0.784

    again this is marked wrong but what is wrong with it?
     
  8. Mar 19, 2017 #7
    I got 0.785 m. Maybe it needs to be a negative number since it hits below the bird.
     
  9. Mar 19, 2017 #8
    it can't be negative, the question is asking for the "distance" which is a scalar quantity. And the question is actually a multiple choice question: The given options are:
    a. 0.43 m
    b. 0.53 m
    c. 0.63 m
    d. 0.73 m
    e. 1.50 m

    I picked 0.73 but that was marked wrong
     
  10. Mar 19, 2017 #9
    I don't know. Sometimes the "correct" answer is just incorrect.
     
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