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It's a question of what to assume.....

  1. Aug 15, 2015 #1
    1. The problem statement, all variables and given/known data
    A water sprinkler sprinkles water all around it. If the velocity of water coming out is v, find the area around the sprinkler getting wet.

    2. Relevant equations
    In projectile motion,
    Range = u^2 sin2(theta) / g

    3. The attempt at a solution
    What I did was to assume each droplet as a projectile with initial velocity v. Looking at it that way, the range of the droplet would be the radius of the circle of area getting wet.
    Everything is fine, except that nothing is mentioned about angle of projection of droplets.
    I assumed 45 degrees and got the right ans. in objective type qn, but if the same comes for subjective explained ans, then which angle do we assume???
    With 45 degrees, my answer was -
    Range = v^2 sin90 / g = v^2 / g
    So area = pi (v^2 / g)^2 = pi (v^4 / g^2)
  2. jcsd
  3. Aug 15, 2015 #2
    I think the original question should read - " What is the maximum possible area covered by the water ? " .

    Considering that , yes , angle taken would be 45° .
  4. Aug 15, 2015 #3


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    You can't assume any angle. The angle must have been omitted from the question by mistake. Alternatively, the question could have asked for the maximum possible area, which then implies 45°.
  5. Aug 15, 2015 #4
    Hmmm....must be a qn error as u say. Anyway, thnx a lot for the help!!!
  6. Aug 15, 2015 #5


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    As I read the intended meaning of the problem, the sprinkler head is spraying randomly at all angles -- a more or less spherical spray. This is weakly implied by the "all around it" clause.
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