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Homework Help: Calculating exit velocity of a projectile

  1. Mar 14, 2010 #1
    I did an experiment using an air cannon to find the drag exhibited on a cylindrical projectile using different mass/density and pressure/velocity. However, I was not able to obtain light gates at the time, so now I have no measurement for velocity. This is necessary for my results, and I was wondering if anyone could help me in calculating it. I have all dimensions and volumes of the components to the air cannon and projectile, distance and time of flight of the projectile, air pressure within the gas chamber and launch angle. If anyone could help me calculate the exit velocity of the projectile it would be greatly appreciated.
     
  2. jcsd
  3. Mar 19, 2010 #2
    im assuming when you say distance thats the range the projectile has gone? if so and you also have the angle then you can use the basic range equation to find the intial velocity.

    range = ((v^2)(sin (2*angle)))/gravity
    so
    v=sqrt((range*gravity)/(sin(2*angle)))

    sorry if i read your question wrong but im in a rush also if my equation doesnt look to neat just search for range equation on google
     
  4. Mar 19, 2010 #3

    hotvette

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    Homework Helper

    By drag, I assume you mean within the cannon itself as opposed to flight drag of the projectile after it exits the cannon. Be careful about using the standard projectile equations to calculate exit velocity based on range and angle. They assume zero drag during flight. Since flight drag is proportional to velocity (or velocity squared I don't remember), you could be introducing unacceptable error into your calcs. Flight drag may nor may not be an actual issue in your case, but you should be aware of it.
     
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