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Homework Help: Projectile question

  1. Nov 13, 2004 #1
    I have attached a diagram of what I am trying to do. This is a side view of a tube that will be carrying that ball up through the curve and back in the opposite direction, just 50 cm higher. The ball is hard plastic and the curved tube is probably going to be hard plastic as well but sprayed w/ teflon. Basically, I need to figure out how much force or energy is required to launch that ball through the tube and out the top.

    I am confused about which formulas apply and which don't. I would appriciate help deriving the formulas so I can tweak the numbers to make this design work best for my project.

    Thanks for the help

    Attached Files:

    Last edited: Nov 13, 2004
  2. jcsd
  3. Nov 13, 2004 #2
    I just want to clarify something. This tube is perpendicular with the ground. The ball is basically traveling straight up, just through this curved tube.

  4. Nov 13, 2004 #3

    Doc Al

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    Staff: Mentor

    If you can ignore energy losses due to friction and the banging of the ball against the tube, then the final KE will equal the initial KE minus mgh (since mechanical energy would be conserved). Thus the ball needs a minimum initial KE = mgh to have a chance of making it. Start with that and tweak it.
  5. Nov 13, 2004 #4
    ok, so the potential energy of the ball once it get to the top of the tube is mgh, (0.03*9.8*.50) = 0.147J. So The Kinetic energy must equal 0.147 J.

    1/2 m v^2 = 0.147 J
    1/2 (0.03kg) V^2 = 0.147j
    v = 3.1305

    Ok thats as far as I can get. Does this means that the minimum velocity must be 3.1305 m/s ?

    Now I know I need to find force required to do this work and eventually use this information to find a solenoid strong enough to do this work. Solenoids list the force they produce in lbs.

    Are these conversions correct to change force to lbs? Is this conversion possible?

    100n = 10kg
    1n= 100g

    thanks for all the help,
  6. Nov 14, 2004 #5

    Doc Al

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    Staff: Mentor

    That's the minimum velocity to barely make it to the top. If you want it to shoot out, you'll need more.

    I'm not sure what your arrangement is, but it's force acting through a distance that will give the ball energy.

    It may be helpful to note that 1 pound = 4.45 Newtons.

    What you've done is find the weight of a given mass using w = mg. For example: a 1 kg mass weighs 1*9.8 = 9.8 N.
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