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Equilibrium and Elasticity problem need help hw due tomarrow

  1. Mar 27, 2008 #1
    [SOLVED] Equilibrium and Elasticity problem need help hw due tomarrow

    1. The problem statement, all variables and given/known data
    two identical, uniform, and frictionless spheres, each of weight W, rest in a rigid rectangular container. A line connecting their centers is at 45° to the horizontal.Find the magnitude of each of the following forces on the spheres in terms of W. (Hint: The force of one sphere on the other is directed along the center-center line.)
    (a) the force from the bottom of the container
    (b) the force from the left side of the container
    (c) the force from the right side of the container
    (d) the force from each other
    here is a diagram of the spheres in the box
    http://www.webassign.net/hrw/hrw7_12-59.gif

    2. Relevant equations
    Newtons second and third laws


    3. The attempt at a solution
    The contact force exerted by the lower sphere on the upper is along that is 45o and the forces exerted by the walls and floors are normal.

    Equilibrium force on the top sphere leads to

    Fwall = F cos 45 and F sin 45 = m g

    According to newtons third law the equilibrium of forces on the bottom sphere leads to

    F'wall = F cos 45 and F'floor = F sin 45 +mg

    a)magnitudes of the forces on the spheres from the bottom of the container

    F'floor = mg +mg = 2mg
    b)magnitudes of the forces on the spheres from the left side of the container

    F'wall = mg
    c))magnitudes of the forces on the spheres from the right side of the container

    F'wall = mg
    d) magnitudes of the forces on the spheres from each other

    F = mg / sin 45 = mg * √2

    but that is incorrect
     
  2. jcsd
  3. Mar 27, 2008 #2

    dynamicsolo

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    Homework Helper

    When you say that the results are "incorrect", are you putting your answers into WebAssign? Don't forget that the weight of each sphere is called 'W', rather than being given as mg. So the machine either wants you to type answers like W, 1.414 W , and 2 W , or just the numbers 1, 1.414, and 2. (I get the same forces that you do.)
     
  4. Mar 27, 2008 #3
    yeah I entered the answers in terms of w but they were still wrong
     
  5. Mar 27, 2008 #4

    dynamicsolo

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    Exactly what did you enter? The force analysis should be right, so we have to figure out just what WebAssign expects to see.
     
  6. Mar 27, 2008 #5
    I figured it out, I did not use a capital w in the answer. thanks for your time.
     
  7. Mar 27, 2008 #6

    dynamicsolo

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    Homework Helper

    WebAssign wouldn't take your answer because it's case-sensitive?!? Don'cha just lloooove computer-based problem systems?
     
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