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Homework Help: Projectiles question: acquiring initial velocity from force+mass

  1. May 13, 2010 #1
    Hello, this may be a rather simple question but it's beginning to irritate me: If I were launching a marble of, say, 10g (0.010 kg) from a marble launcher with a force of 5N (tell me if this is realistic or not) at an angle of 15 degrees then how would I go about finding the initial velocity of the marble?

    Please tell me if I was taking to this question in the correct manner:
    I first split the force F into it's horizontal and vertical components:

    I then found, using F= m * a, the initial horizontal and vertical acceleration:
    Ax = 483
    Ay = 129

    This is the point I was truly having trouble with, finding the initial vertical and horizontal velocities:

    To do this, I assumed that since the initial velocity are found at the moment all of the force is transfered to the marble:

    Vx = Ax
    Vy = Ay

    Is this true?
  2. jcsd
  3. May 13, 2010 #2


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    Science Advisor
    Homework Helper
    Gold Member

    You are missing a key number which is how long the force acts on the marble. The longer it acts the higher the initial velocity upon launch. That's because acceleration is a=F/m and v = at = Ft/m.
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