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Homework Help: AP Physics Summer work problems!

  1. Aug 22, 2008 #1
    1. The problem statement, all variables and given/known data

    Assuming you have a bow that behaves like a spring with a spring constant of 168 N/m and you pull it to a draw of 54 cm, to the nearest joule how much work do you perform?

    2. Relevant equations

    The force of a constant spring is f=-k(x) where x is the displacement and k is the spring constant.

    3. The attempt at a solution

    So Basically If I find the force and then place it into the simple work equation W=F(x) where x is displacement and F is force. I get 49(rounded). Am I doing this correctly?
  2. jcsd
  3. Aug 22, 2008 #2
    There's an equation for potential spring energy... it looks similar to the kinetic energy equation, but with different variables.
  4. Aug 22, 2008 #3
    Welcome to the forums Iammaskier,

    Yes, it looks like you are doing it correctly to me. Basically, W = k*x^2 in this case.

    Ok, but what does that have to do with this problem?
  5. Aug 22, 2008 #4
    Is use that equation of u=1/2kx^2 and got 24.4944 joules. How does that convert to the work performed?
  6. Aug 22, 2008 #5
    Another quick question! There is a second part which is... to the nearest tenth of a m/s, what is the speed of the 98 gram arrow when it is released?

    I know I have to find the velocity but I have no clue how to do it.

    I've never taken physics before and it's decenlty hard to teach yourself=/
  7. Aug 22, 2008 #6
    This link shall explain why you simply can't use W=kx^2, but instead W=.5kx^2

    http://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.emporia.edu/physics/keithron/collegelab1/hooklaw.htm [Broken]
    Last edited by a moderator: May 3, 2017
  8. Aug 22, 2008 #7
    And of course, once you realize that, then the second part to your problem should become quite easy if you understand the conservation of energy, as well as a comparison I made in my initial reply regarding another similar looking equation.
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