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Homework Help: Friction involving cylinder

  1. May 5, 2010 #1
    1. The problem statement, all variables and given/known data

    see attachment

    2. Relevant equations

    see attachment

    3. The attempt at a solution

    I understand everything about the problem except how to determine the angle P makes with the new horizontal axis (parallel with F)--see diagram under primary one... so that I can sum the forces up and answer the problem. My geometry is somewhat rusty and I'm not exactly sure what geometric property makes the angle 45. Any help is appreciated.

    Attached Files:

  2. jcsd
  3. May 5, 2010 #2
    Your solution looks correct to me. You summed the moments at B to get P=812 nt. You resolved the Ff and N into components in the x and y direction (all the angles look to be 45 degrees). You summed the forces in the in the x and y direction =0 and solved for mu.
  4. May 22, 2010 #3
    HELP me on this problem please it involves a cylinder and i cant figure out the correct solution.
    (see attachment)

    Here is the question:

    Determine magnitude of force P that will cause the cylinder rotates.

    Weight of Cylinder = 400N
    Radius of Cylinder = 150mm
    Coefficient of friction in all surfaces is = 0.2

    Attached Files:

  5. May 22, 2010 #4
    I would draw a free body diagram of the cylinder. There will be normal and frictional forces on the A and B surfaces. Resolve P into X & Y directions. One of the things you will need to convince yourself of, by geometry, is if a line segment drawn from the origin (where A & B meet) through the center of the circle and connecting to P is a 90 degree angle. If it does you can take the moment about the origin and get rid of some of the ugliness relating to the frictional forces. Summing forces in the X & Y directions plus the moment equation should give you enough equations to solve the problem.
  6. May 23, 2010 #5
    can you please help me setup the equation or can u illustrate the proper solution for this problem i really don't know how to start with please help i need solution thanks,
  7. May 23, 2010 #6
    Have you done a free body diagram of the cylinder, that is the first step? Choose a coordinate system such as the directions of sides A and B. Resolve the P force in the direction of the coordinate system you have chosen. P is the hypotenuse of a 3-4-5 triangle so you know all the angles associated with P. Sum the forces in the x, y direction and take the moment about the origin. You will end up with 3 three equations and 3 unknowns one of which is P. You can use your knowledge of linear equations to solve for the three unknowns.
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