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Cannonball is catapulted

  1. Sep 15, 2011 #1
    1. The problem statement, all variables and given/known data:A cannonball is catapulted toward a castle. The cannonball's velocity when it leaves the catapult is 34 m/s at an angle of 55° with respect to the horizontal and the cannonball is 8.0 m above the ground at this time.
    (a) What is the maximum height above the ground reached by the cannonball?


    (c) What are the x- and y-components of the cannonball's velocity just before it lands? The y-axis points up.


    2. Relevant equations
    Maximum height = Yf=Yo+Voy*t+1/2gt^2
    Voy=34sin55=27.85 m/s
    Vf=Vo+at=0=27.85-9.8t t=2.8s
    Maximum height= 47.56 m
    How do I find the x and y components? what equations do I need?
     
  2. jcsd
  3. Sep 16, 2011 #2

    vela

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    You only have a handful of equations for projectile motion. What other ones do you have?
     
  4. Sep 16, 2011 #3

    BruceW

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    Are we on to part (c) now? Well, you've already got the equation for y as a function of t. From this you can get t. Then you can use t in the velocity equations.

    There are no forces in the x-direction, so what will the equation for x component of velocity be? And for y-direction, there is constant force, which you already have the equation for.
     
  5. Sep 16, 2011 #4
    Could you explain why my maximum height is wrong please?

    I dont know that equations for part see...
     
  6. Sep 16, 2011 #5

    BruceW

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    Oh, yeah. Your max height is wrong, I didn't see that.

    Well, your time for maximum height (2.8s) is correct. So you just need to put this into your equation for the height to get the maximum height.
     
  7. Sep 16, 2011 #6

    vela

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    The last term in the equation for yf should have a negative sign in front of it, which you apparently used in your calculations. If you're entering the answer into the computer and it's marking it as wrong, you're probably entering it incorrectly. Perhaps you left the units off or you're using the wrong number of significant figures.

    Well, what are the equations you have for projectile motion? Surely, you can find them in your book and tell us what they are. Then we can help you figure out which ones are the best to use.
     
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