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Math Help - Physics - Friction

  1. #1
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    Physics - Friction

    A block weighing 21 N is held at rest against a vertical wall by a
    horizontal force of magnitude 59 N. The coefficient of static
    friction between the wall and the block is 0.56, and the coefficient of
    kinetic friction between them is 0.37. A second
    force is applied to the block and directed parallel to
    the wall with this magnitude and direction: 62 N, up. What is the
    frictional force on the block, including sign? Take the direction up the
    wall as positive, and down the wall as negative. Next, calculate the
    acceleration, including sign, of the block.


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  2. #2
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    Quote Originally Posted by anywho View Post
    A block weighing 21 N is held at rest against a vertical wall by a
    horizontal force of magnitude 59 N. The coefficient of static
    friction between the wall and the block is 0.56, and the coefficient of
    kinetic friction between them is 0.37. A second
    force is applied to the block and directed parallel to
    the wall with this magnitude and direction: 62 N, up. What is the
    frictional force on the block, including sign? Take the direction up the
    wall as positive, and down the wall as negative. Next, calculate the
    acceleration, including sign, of the block.
    Horizontal force is balanced by the normal reaction from the wall. Since the block is at rest, frictional force must be equal to 21 N acting in the upward direction.
    when the block is pushed up, Net force acting on it is
    P - mg -μ(k)*N = m*a
    Now find a. Here m = (21/g) kg
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