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Homework Help: Kinetic Energy Question

  1. Oct 4, 2007 #1
    A 47.7-g golf ball is driven from the tee with an initial speed of 55.4 m/s and rises to a height of 31.2 m. (a) Neglect air resistance and determine the kinetic energy of the ball at its highest point. (b) What is its speed when it is 8.47 m below its highest point?
     
  2. jcsd
  3. Oct 4, 2007 #2

    hage567

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    Homework Helper

    What have you tried? You need to show some effort. What equations/concepts might apply here?
     
  4. Oct 4, 2007 #3
    K = (1/2)mv^2 and i need something to help deal with the height part
     
  5. Oct 4, 2007 #4

    hage567

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    Do you know about gravitational potential energy?
     
  6. Oct 4, 2007 #5
    U=mgh... 47.7(-9.8)31.2 =14584.754 = U or gravitational potential energy
     
  7. Oct 4, 2007 #6

    Doc Al

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    Mechanical energy (KE + PE) is conserved. Careful with units. (The mass is given in grams, not kg.)
     
  8. Oct 4, 2007 #7
    .0477(-9.8)(31.2) = -14.584752
     
  9. Oct 4, 2007 #8
    wouldnt kinetic be 0 at the highest point because all the energy is potential?
     
  10. Oct 4, 2007 #9

    Doc Al

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    No. Only the vertical component of velocity is zero at the highest point--it's still moving horizontally.
     
  11. Oct 4, 2007 #10
    what do i do now?
     
  12. Oct 4, 2007 #11

    Doc Al

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    Compare the initial energy (KE + PE) at the start with the energy (KE + PE) at the top. The ball loses KE as it gains PE.
     
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