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Homework Help: Finding the speed of the bob?

  1. Dec 14, 2014 #1
    1.) The problem statement, all variables and given/known data
    A(n) 2.71 m long pendulum is released from rest when the support string is at an angle of 35.8◦ with the vertical.
    The acceleration of gravity is 9.8 m/s2 . What is the speed of the bob at the bottom of the swing?
    Answer in units of m/s

    2.) Relevant equations
    Not sure

    3.) The attempt at a solution
    I tried to do 2.71sin(35.8) and I got 1.585. It's not the right answer. I also tried to do do cos(35.8) but that did not work either. Are there any other equations I have to use to find the speed of the bob?
  2. jcsd
  3. Dec 14, 2014 #2


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    Staff: Mentor

    Where does the energy come from that results in the bob having a velocity?
  4. Dec 14, 2014 #3
    Does the energy come from the string?
  5. Dec 14, 2014 #4
    The best way to solve is to draw a neat diagram and show all the forces acting on the object. This might seem trivial but helps in better understanding of many concepts of physics.
  6. Dec 14, 2014 #5


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    What would the result of that calculation represent? What would its units be?
  7. Dec 15, 2014 #6
    since 2.71 is m I assume it would be m as well not m/s.
  8. Dec 15, 2014 #7


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    Right, so it is not a speed.
    What do you know about potential and kinetic energy? Any equations you know of?
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