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Homework Help: Motion In Two Dimensions Lab Question

  1. Oct 2, 2008 #1
    Question and Data
    What is the initial velocity of an object that rolls off a table and hits the floor below?
    Lab produced the following data:
    Table height: 86 cm
    Distance of object from table when it hits floor: 23 cm

    Relevant equations
    Instantaneous Speed: Vf = Vo + at
    [I think this is the correct one...]

    The attempt at a solution
    Gravity affects the object at a rate of 9.8 m/s.
    Converting dimensions to meters:
    86 cm = .86 m
    23 cm = .23 m
    I know gravity affects the height and the velocity affects the distance from the table and these two do not affect each other, but how do I determine the time?
    You can't use sin and that triangle stuff because the object arches, it isn't straight.
    I'd applicate any help or hints you could provide to help me threw this problem.
  2. jcsd
  3. Oct 2, 2008 #2


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    Homework Helper

    Welcome to PF.

    First figure the time for the object to fall .86m

    x= 1/2g*t2

    Then you know how far it went and for how long so figure how fast the horizontal velocity was and you're done.
  4. Oct 2, 2008 #3
    Thank you.
    x would really be the y displacement, which is .86m, correct?
    So time is .419 seconds... and would you plug that into the displacement & time equation?
    Which would give you 1.504 m/s as the initial velocity.

    Thank you for your help.
    Last edited: Oct 2, 2008
  5. Oct 2, 2008 #4


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    Homework Helper

    Isn't the distance .23m and the time .419s?
    I get something quite less than 1.5 m/s at constant velocity.
  6. Oct 3, 2008 #5
    If your looking for the x displacement. It turns out the same either way.
    But yes, it is less than 1.5m/s. It's around .6, if I remember correctly. I plugged in gravity for the acceleration the second time but it's zero because their is no horizontal acceleration.

    Thank you very much for your time.
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