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Homework Help: Friction-less wedge physics problem

  1. Sep 26, 2004 #1
    A 2.0-kg body rests on a frictionless wedge that has an inclination of 65.0° and an acceleration a to the right such that the mass remains stationary relative to the wedge. Find a

    This is one of the question i had to do for HW.
    Not really asking for an answer but it would be great if you provide one with a semi detail equation

    I just don't get how is a body at rest yet accelerating!! I probably misinterpret the question and I hope someone will point out where I misunderstood. Thank You
    Last edited: Sep 26, 2004
  2. jcsd
  3. Sep 26, 2004 #2
    What they mean is that the wedge with the mass on it is being acclerated (along the floor, for example) in a way that the mass does not slide down the wedge as it would if it were stationary. Try using some basic principles. Very interesting problem.
  4. Sep 26, 2004 #3
    Thx for pointing out my misinterpertation ^_^. Now, the question made more sense.

    Ok, I tried doing the question but I got the wrong answer :mad: and this is what I did:

    I thought maybe mass doesn't matter in this situation cuz all object has the same accelartion due to gravity
    so i just went acelaration to the right = 9.8 x sin 65 x sin 25

    The sin 65 was to find the accelartion for the body sliding down the incline
    this accleration is parallel to the incline

    Then i did a bit of geometry to figure out that sin 25 will give me "a" to the right.

    so, was i wrong about ignoring the mass or what?
  5. Sep 26, 2004 #4


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  6. Sep 27, 2004 #5

    Doc Al

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    I'm afraid so. :smile:
    In any problem concerning acceleration or force, you'd better consider the mass.

    Think this way. There are two forces acting on the body: (1) the normal force from the wedge, and (2) the weight. Hint: in the vertical direction, the body does not accelerate; in the horizontal direction, it does. Apply [itex]\vec{F_{net}} = m \vec{a}[/itex].
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