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Homework Help: Vectors and Velocity Problem

  1. Mar 19, 2010 #1
    1. The problem statement, all variables and given/known data
    The ball is moving at 2.0m/s just 40cm before it hits the table edge. If the ball has a mass of 51.3 grams and experiences a 0.23 N frictional force between it and the table, how fast will it be moving when it reaches the table's edge?

    The table is 0.92m tall. How long will it take the ball to hit the ground?


    2. Relevant equations

    X=Xo+Vot+(0.5)at2
    Y=Yo+Voyt+(0.5)at2
    X=Xo+Voxt
    FNET=ma
    Fg=mg
    Quadratic Formula


    3. The attempt at a solution

    I used FNET=ma to solve for the acceleration and got -4.48m/s2. Then I used X=Xo+Vot+(0.5)at2 and the quadratic formula to solve for t and got 0.3 sec. I then plugged this into V=Vo+at to get a velocity of 0.656m/s. Is this correct?

    For the second question: I have that it will take 0.09 sec for the ball to hit the ground and it will land 0.1719 meters away from the table.
    Does this seem correct?

    Thanks in advance for any help.
     
    Last edited: Mar 19, 2010
  2. jcsd
  3. Mar 20, 2010 #2

    rl.bhat

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    Homework Helper

    In the first part, if you use
    vf^2 = vi^2 - 2*a*s, you get slightly different vf value.
    In the second part, your t value is wrong. In that case the initial velocity in the vertical direction is zero.
     
  4. Mar 21, 2010 #3
    So if I were to set up a variable list for how long it will take the ball to hit the ground would it look like the following?

    Xo=0m
    X=?
    Vox=1.91m/s
    t=?
    Yo=0.92m
    Y=0m
    Voy=-9.8m/s
    g=-9.8m/s2

    Using these values I got 0.09 seconds. But that does not seem right...
     
  5. Mar 21, 2010 #4

    rl.bhat

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    Yo=0.92m
    Y=0m
    Voy=-9.8m/s This is not correct. It should be zero.
    g=-9.8m/s2
     
  6. Mar 21, 2010 #5
    So I have redone this problem making some corrections and have come up with these answers:

    -When the ball reaches the table's edge it will be moving 0.65m/s.
    -It will take the ball 0.44 seconds to hit the ground.
    -The ball will land 0.286 meters away from the table?

    Have I gotten this problem correct?

    And if I were to graph my y-component velocity, would it be a constant 0m/s?

    Thanks!
     
    Last edited: Mar 21, 2010
  7. Mar 21, 2010 #6

    rl.bhat

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    -It will take the ball 0.44 seconds to hit the ground.
    Time t is 0.43 s.
     
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