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    abailey2011's Avatar
    abailey2011 Posts: 2, Reputation: 1
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    #1

    Apr 17, 2014, 09:21 AM
    Physics Question 1
    A window washer pushes his brush up a vertical window at constant velocity by applying a force F as shown below. The brush weighs 12N and the coefficient of kinetic friction is 0.2. Find the magnitude of force F
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Apr 17, 2014, 11:12 AM
    Hint: since the brush moves at constant velocity the sum of forces acting on it must equal zero.
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    CWH68 Posts: 26, Reputation: 2
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    #3

    Apr 17, 2014, 01:29 PM
    He pushes it up with a force of 12N, to cancel the force of gravity.
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    ebaines Posts: 12,131, Reputation: 1307
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    #4

    Apr 17, 2014, 02:44 PM
    I think not - the OP mentioned friction. Without seeing the diagram it's impossible to answer.
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    CWH68 Posts: 26, Reputation: 2
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    #5

    Apr 17, 2014, 03:33 PM
    True. The angle of the brush is not known. Call it a. Then,

    F = 12N / (cos a - 0.2 sin a) provided tan a < 5. Otherwise, he cannot push the brush up.

    P. S. a is the angle of the brush from the vertical.
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