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Homework Help: 2 Problems: 1 friction 1 uniform acceleration

  1. Sep 25, 2005 #1
    Hey folks,

    If someone can take a look at these two homework problems and help me out, it'd be greatly appreciated.

    1) A box of Cheerios and a box of Wheaties are accerelated across a horizontal surface by a horizontal force F applied to the Cheerios box. The magnitude of the frictional force on the Cheerios box is 2.0 N and the magnitude of the frictional force on the Wheaties box is 4.0 N. If the magnitude of F is 12.0 N, what is the magnitude of the force on the Wheaties box from the Cheerios box?

    The Cheerios box is 1.0 kg and the Wheaties box is 3.0 kg.

    The first thing I did was come up with all the forces on the boxes:

    Wheaties Box:
    \Sigma F_{x} = F_{c}-F_{fric, w} = m_{w}a[/tex]
    [tex]\Sigma F_{y} = N_{w}-m_{w}g = 0

    Cheerios Box:
    \Sigma F_{x} = F-F_{fric, c} = m_{c}a[/tex]
    [tex]\Sigma F_{y} = N_{c}-m_{c}g = 0

    Then I used the first equation to solve for [tex]F_{c}[/tex]. I got: [tex]F_{c}=m_{w}a - F_{fric, w}[/tex].

    I then plugged in for the acceleration (using the 3rd equation) and my final answer is: 26 Newtons. Does that sound right to anyone? It seems a bit high which is why I ask.

    2) An old street car rounds a corner of radius 9.1 m, at 16 km/h. What angle from the vertical will be made by the loosely hanging hand straps?

    I didn't get far enough with this one to do much work, but my initial thought is that there is some kind of force acting in the horizontal direction that would push the hand straps. I'm not sure what it is or where else to begin with this.

    Thanks a bunch!
  2. jcsd
  3. Sep 25, 2005 #2


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    If C pushes on B , doesn't B push back on C ?

    The hand strap is connected to the street car
    at the ceiling. The street car is accelerating.
  4. Sep 25, 2005 #3
    So does that mean that there should be an extra force on the Cheerios box, from the Wheaties box, in the opposing (same as friction) direction?
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