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Homework Help: How to calculate the speed of an object attached to a string

  1. Dec 5, 2017 #1
    1. The problem statement, all variables and given/known data
    The question and the known/given variables are on the image in part 3. The question says that a 20-g bead is attached to a light 120 cm-long string. Now in my mind the bead will travel in a circular path if it is pushed really hard. So Isn't the length of the string, 120 cm, the radius of the circle? In my work, I had to solve for the radius. I found a solution online and this is their work. The correct answer is 1.1 m/s.

    2. Relevant equations
    It's in part 3 in the image.

    3. The attempt at a solution
  2. jcsd
  3. Dec 5, 2017 #2


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    2017 Award

    Staff: Mentor

    The bead rotates in 3 D while keeping its height. It is not a typical pendulum. The r in the lower left part of the image is the horizontal separation of the object - the radius of the horizontal motion. It is a bit confusing that the same variable name is used again.

    Edit: Picture for future reference:
    physics question.jpeg
    Last edited: Dec 5, 2017
  4. Dec 5, 2017 #3
    Wow, it makes so much sense now! Thanks!!!!
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