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Homework Help: What is the speed of the ball just before it strikes the ground?

  1. Sep 13, 2010 #1
    A ball is thrown from the top of a building
    upward at an angle of 47 ◦ to the horizontal
    and with an initial speed of 23 m/s, as in
    the figure. The ball is thrown at a height of
    46 m above the ground and hits the ground
    82.0127 m from the base of the building.
    The acceleration of gravity is 9.8 m/s2 .

    What is the speed of the ball just before it
    strikes the ground?
    Answer in units of m/s.


    I have tried calculating the max height (14.4363m) and the time @ max height (1.71644s) then doing vf-=vi-gt => vf=-9.8(1.71644)=-16.8211 m/s (wrong)

    not sure what else to try...
     
  2. jcsd
  3. Sep 14, 2010 #2
    I'm not sure how you managed to get max height at 14.4363m when the ball is ''thrown at a height of 46 m above the ground.'' Try redrawing your diagram, I can show you how to get answer, just tell me if the answer is v=56.16m/s otherwise I will have to recheck my drawing.

    Best of luck
     
  4. Sep 14, 2010 #3
    the answer is not v= 56.16 m/s

    thanks though
     
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