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Homework Help: Quick questions on work

  1. Nov 4, 2007 #1
    1. The problem statement, all variables and given/known data
    Tarzan swings on a 34 m long vine initially inclined at an angle of 41 degrees with the vertical.
    The acceleration of gravity is 9.81 m/s^2.
    What is his speed at the bottom of the swing if he starts from rest?
    What is his speed if he pushes off with a speed of 4 m/s?

    2. Relevant equations
    w=(f)(d)(cos theta)
    w= KEF - KEI

    3. The attempt at a solution
    I got the work, but how can you possibly find out his speed if a mass is not given? I'm thinking that it might have something to do with the kinetic energy equation, but you need mass for that. I'm not really sure of what to do now. I have a similar question like this, but with a loop-the-loop, which also does not give a mass. Someone please help!
  2. jcsd
  3. Nov 4, 2007 #2
    Please help, I am really lost.
  4. Nov 4, 2007 #3
    Maybe someone can help me with a more difficult problem if no one is going to answer anything from above.

    A student performs a ballistic pendulum experiment using an apparatus similar to that shown in the figure.
    Initially the bullet is fired at the block while the block is at rest (at its lowest swing point). After the bullet hits the block, the block rises to its highest position (3 cm), and continues swinging back and forth.
    max height : 3 cm
    max height subtend angle: 36.9 degrees
    mass of bullet : 99 g
    mass of pendulum bob: 825 g
    accel of gravity: 9.8 m/s^2

    Detrmine the initial speed of the projectile. Answer in units of m/s.
  5. Nov 4, 2007 #4


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    Science Advisor
    Homework Helper
    Gold Member

    You should instead be looking at the conservation of energy equation (which will include a potential energy term).
  6. Nov 4, 2007 #5
    I know the equation, but I don't understand where you are going with it.
  7. Nov 4, 2007 #6
    Forget it, my peers figured out the equations necessary for the problems I could not answer while I was at work. Thanks anyway.
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