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Long Jump Question

  1. Oct 20, 2009 #1
    1. The problem statement, all variables and given/known data

    A runner jumps at 30 degrees to the ground and covers 8.90 m. What was the takeoff speed?


    3. The attempt at a solution

    I have no idea where to start...
     
  2. jcsd
  3. Oct 20, 2009 #2

    rl.bhat

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    Resolve the velocity in to vertical and horizontal components.
    What happens to these components with respect to time?
     
  4. Oct 20, 2009 #3
    how would i go about solving the velocity for each component?
     
  5. Oct 20, 2009 #4

    rl.bhat

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    If v is the velocity what are the vertical and horizontal components?
     
  6. Oct 20, 2009 #5
    honestly, i have no idea
     
  7. Oct 20, 2009 #6

    rl.bhat

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    Open any text book. And refer the motion in two dimension.
     
  8. Oct 20, 2009 #7
    but all i have is the angle of the jump and the distance...no time or anything
     
  9. Oct 20, 2009 #8

    rl.bhat

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    Using proper equation you can find the remaining unknown quantities. Try to find out the equations.
     
  10. Oct 20, 2009 #9
    do u mean these formulas?

    Fx = cos A * F1
    Fy = sin A * F1
     
  11. Oct 20, 2009 #10
    honestly, im struggling and have no idea what to do...
     
  12. Oct 20, 2009 #11

    rl.bhat

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    Yes. These are the two components. Only replace F by v for the velocity.
    In that x component remains constant, because there is no acceleration in that direction. If t is the time of flight, then x = vcosθ*t.
    In the vertical direction, the initial velocity is vsinθ. What is the final velocity when it reaches the maximum height. And what is the time taken to reach the maximum height?
     
  13. Oct 20, 2009 #12
    when u say x = vcosθ*t , what is v? the speed before the jump?
     
    Last edited: Oct 20, 2009
  14. Oct 20, 2009 #13

    rl.bhat

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    No. You have to find out. I have told you to write down all the kinematic equations. Then I will tell you which equation to be used to find the time.
     
  15. Oct 20, 2009 #14
    oh wouldnt the final velocity be 0 when it reaches a maximum height? because he would have stopped moving up?
     
  16. Oct 20, 2009 #15

    rl.bhat

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  17. Oct 20, 2009 #16
    I dont know how to find the time it would take to reach the max height.
     
    Last edited: Oct 20, 2009
  18. Oct 20, 2009 #17

    rl.bhat

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    Why can't you write down all the relevant kinematic equation. In the post submitted to PF, this is the second requirement.. You have not submitted that. Do it first now.
     
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