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Homework Help: Projectile Motion Lab.

  1. Oct 1, 2006 #1
    We are doing a Lab on Projectile motion:

    It is where you take a ball and roll it off a ramp, off the table. Then you would need to estimate the precise landing spot on the ground.

    Directions: You are given the height of the table, but not the distance or the velocity of the ball rolling down. What you need to find is the distance (displacement of the ball from the table to the ground).

    I have looked over many problems like this and I have solved examples many times and were correct. However, how do you find the velocity of the ball? My teacher said you don't really need the velocity to calcuate the distance but how??

    Is this how you calculate the horizontal velocity of the ball coming down a ramp?

    PEtop = KEbase
    mgh = ½mv^2
    2mgh = mv^2
    square root( 2gh) = v

    So would the velocity equal the sqr root(2(-9.8m/s^2)(h))???
    Does the average horizontal velocity always equal that no matter how big the mass of the ball/marble is?? Please explain. Thanks.

    After I know the velocity, I will be able to solve the lab, I just need to know if that equation is correct or not, and why. We haven't gone over PE and KE stuff.. Thanks a lot! :biggrin:
  2. jcsd
  3. Oct 1, 2006 #2
    yes, you have the right equations
  4. Oct 1, 2006 #3
    by the way, the h (height) is suppose to be the height of the RAMP not the height of the table. Is this equation correct for finding the velocity of any ball/sphere/marble rolling off the ramp??

    I just need to find the velocity of the ball rolling down the ramp. I don't know if the equation is valid or not for it. I mean does it apply to all balls no matter what their mass is? If you look on the lab website, it says that the masses cancel out and therefor remain with: v= sqr. rt. (2gh)

    Does anyone know if this equation is good for any ball with any kind of mass? If you need to see the lab, it is on the top of the page.
  5. Oct 1, 2006 #4
    ok thanks, but I need more confirmations.. Anyone else??
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