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Homework Help: Desperate help needed for Projectile motion!

  1. Aug 21, 2005 #1
    Hello everybody! My name is Nazia, and I’m from Australia . This is my first post, so please let me know if I do something wrong.

    I’m 15 and in grade 11. I seem to be having problems with Projectile motion.

    Recently, we were required to conduct an experiment, in which a marble was launched off a ramp. The ramp was a had two parts, one an incline was connected to horizontal tube, which was connected the to a tube that was elevated by 45 degrees of the bench.

    The ramp kind of looks like this:

    ( the left side lines are meant to be connected, to from one straight line)

    I’m having trouble calculating the initial velocity it leaves the ramp with. I’ve done only problems where the initial velocity was horizontal. However in this problem the initial velocity will have two components right?

    Does anyone have any suggestions how I work out the intial velocity??


    Has it got something to do with, a loss in Potential energy equals a gain in Kinetic??
    Last edited: Aug 21, 2005
  2. jcsd
  3. Aug 21, 2005 #2


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    Gold Member

    If you are assuming that the losses to friction, air resistance, etc., are negligable, then the loss in potential energy will equal the gain in kinetic energy, like you suggested, and this should solve the problem. Keep in mind that the change in height is not the change from the highest point to the lowest point, but from the top of the ramp to the height at which it leaves the ramp. The velocity will have two components. Solving the kinetic energy equation will give the speed of the ball. If this is what you want, you can stop here. If you want the horizontal component, multiply by the cosine of the angle between the horizontal and the velocity of the ball.
  4. Aug 21, 2005 #3


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    Science Advisor

    You will, of course, need to use a little trigonometry to find the difference in heights between the initial and final points. You say that the last incline is at 45 degrees. You will also need to know the slope of the first incline and the lengths of the two inclines. As long as you are ignoring friction, the length of the horizontal middle section is irrelevant.
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