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Falling coffee mug, time of descent

  1. Mar 29, 2008 #1
    1. The problem statement, all variables and given/known data

    A customer slides an empty coffee mug down the counter. The employee is momentarily distracted and does not see the mug, which slides off the counter and strikes the floor 1.9m from the base of the counter. The height of the counter is .840m.
    a. With what velocity did the mug leave the counter?
    b. What was the direction of the mug's velocity just before it hit the floor?

    2. Relevant equations



    3. The attempt at a solution

    a. I'm not sure how to find the velocity. Would I use one of the kinematic equations?


    b. Theta=tan-1(.840/1.9)
    =23.85

    360-23.85=336 below the horizontal axis

    Thank you very much
     
  2. jcsd
  3. Mar 29, 2008 #2
    You have two situations, one in the x-direction, and one in the y-direction. Figure out the time it takes the coffee mug to fall x metres in the x-direction. You can then plug that time into an equation relating the distance travelled in the y-direction, the time, and the initial velocity in the y-direction. From this you can get the initial velocity of the mug. You can also get the final velocity in the y-direction of the mug, and then find your angle that way.
     
  4. Mar 29, 2008 #3
    Thank you very much

    Would I use this equation?

    xf=vxi+1/2axt

    (Figure out the time it takes the coffee mug to fall x metres in the x-direction) Would I use one of the kinematic equations?

    I'm looking for the final velocity, right?

    Thank you
     
    Last edited: Mar 29, 2008
  5. Mar 29, 2008 #4
    What would be your a then? Do you have an acceleration in the x-direction? Last time I checked, gravity worked down towards the centre of the earth. ;)
     
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