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Help with Constant Acceleration Lab

  1. Oct 17, 2003 #1
    [SOLVED] Help with Constant Acceleration Lab

    Hey guys, thanks for reading my post. I'm really confused about a lab that was assigned by my teacher. I will try to explain the whole lab the best I can.

    Lab: The Balls Lab

    Purpose of the Lab: To determine the initial velocity (Vo) and maximum height (dy) of a thrown (and hit) ball

    Materials: tennis ball, tennis racket, stop watch
    1. Throw a ball straight up into the air
    2. Measure the time the ball is in the air and comes down
    3. Due three trials

    Data: (here are the 3 time results I got for the ball)
    Trial 1- 3.21 seconds
    Trial 2- 3.10 seconds
    Trial 3- 2.94 seconds
    Average- 3.08 seconds

    Hitting the ball with tennis racket
    Trial 1- 1.41 seconds
    Trial 2- 2.88 seconds
    Trial 3- 1.87 seconds
    Average- 2.05 seconds

    Ok here is the problem... I have no clue how to start solving for the initial velocity (Vo) for the average of the ball thrown and hit in the air. At first I thought the initial velocity of the thrown ball was 0 because that is usually the velocity of any object at rest and then going into the air. But my teacher said it wasn't because he wanted the intial velocity from when it left my hand not when it is at rest, which is 0. He also told me that I needed to use one of the equations of motion for constant acceleration such as: Vf=Vo+at, d=1\2(Vf+Vo)t, d=Vo=1/2at(squared), or 2ad=(Vf)squared-(Vo)squared and the acceleration of gravity, -10 m/s to solve for Vo. But he wasn't clear on which one. Also it seems to me that each of these equation require the value of Vo itself! I am also very confused at how to find the height of the thrown ball (dy) because y is not given as a variable in any of these equations.

    If you guys can show me how I can solve for the initial velocity (Vo) and the maximum height(dy) of the of the ball thrown using any of the equations above or even your own methods, please enlighten me with you explanation. I am most grateful.

    Thank you for taking the time to answer.
    Last edited by a moderator: Oct 17, 2003
  2. jcsd
  3. Oct 18, 2003 #2

    Initial velocity:
    You must think what is the relation between the time that the ball goes up and the total time of the movement you have measured. Then you must think what happens to the velocity of the ball when it reaches the highest spot of its orbit. With the above data and the proper equation of motion you can calculate the initial velocity.

    Height of the throw:
    You have calculated the initial velocity so the only thing you need is the time that the ball needed to get from your hand to its highest spot.

    Sorry, I don’t give you the exact equations and values of time and velocity but if you fallow the steps I have written above I am sure that you will solve the problem by your own. You must think if you want to gain knowledge and on the other hand you will feel so great when you find the solution.

    Excuse me for the sermon.
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