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Homework Help: A 5.0 kg block pushed 3 m up a vertical wall

  1. Oct 22, 2005 #1
    This 5.0 kg block is pushed 3.0 m up a vertical wall with constant speed by a constant force of magnitude F applied at an angle of theta = 30 degrees with the horizontal. mu kenetic = .30 between wall and block. I need to a). determine the work done by F, b) the force of gravity and c) the normal force between block and wall, and d) by how much does the gravitational potential energy increase during the blocks motion?
    I think I figured out the triangle as follows: x element is 2.28, y element (of course) is 3.0 m , and r = 4.56. I'm not even sure if those are correct. In any case, the normal force would be zero because its vertical, right? So, the force of mass X gravity is one force, plus the force applied, and the friction must be taken into account.
    Don't I need to solve for the F first, before finding work? I wish this were easier for me!!! I have more homework than this, and its taking all day!!!
    Thank you for your help!
  2. jcsd
  3. Oct 23, 2005 #2


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    Find the force F first, yes.

    Resolve the force F into horizontal and vertical components.
    Since the movement is with constant velocity, that means there is no acceleration therefore no net force. i.e. all the forces must balance.

    If you balance the horizontal and vertical forces, you should be able to solve for F.
  4. Oct 23, 2005 #3
    Ok, lets give this a try:
    F horiz = n-w sin 60 degrees n= normal force, w = weight (mg)
    F vert = mg(mu) m= mass, g= gravity mu = .30
    so, I set them equal to each other?
    F horz = F vert
    Is this the right track? Thank you for helping, I feel like I'm getting really close to understanding this thing.
  5. Oct 23, 2005 #4


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    I'm afraid not :frown:
    That may have been my mistake. When I said
    I didn't mean with each other.

    When the horizontal forces, say, balance, that means that they (the horizontal forces) balance with each other. All the forces acting to the right balance (are equal to) all the forces acting to the left.

    [tex]\Sigma F_{horiz} = 0[/tex]
    [tex]N - Wsin(60) = 0[/tex]


    [tex]\Sigma F_{vert} = 0[/tex]

    You need to find all the vertical forces acting on the block. Then balance them. All the upward acting forces are equal to all the downward acting forces.
  6. Oct 23, 2005 #5
    OK, I got it now

    Thank you, I think I have it now. I appreciate your help.
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