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Homework Help: 1 Simple Question.

  1. Jan 12, 2008 #1
    My physics exams are on monday.
    I'm going to a univecity and i've never seriously studied physics up to now. I'm making baby steps into learning some of the basics i've never learned.

    I've got this one Review Problem i'm having problems solving.

    Info : g=10ms^-2 Sin30=0.5 Cos30=0.866

    A box of mass m = 50 kg is initially at rest at point A on a floor with coefficient of kinetic friction μk = 0.1 (see figure below). A person starts pulling the box for a distance Δx = 40 m (from point A to point B) with a force FP = 100 N which acts at a 30o angle as shown in the figure and the box moves horizontally.

    a) Draw the free-body diagram of all forces acting on the box

    Drawing the Free body diagram is easy, i dont need help on this one actually.

    b) Find the normal force FN on the box

    Need help :(

    c) Find the friction force Ffr on the box

    If i'd only knew how to find FNormal :(

    d) Calculate the acceleration a of the box

    a=FNormal / m ( m = mass )
    Sin30= FpY/FP = 0.5 (FPY, Y is the Y axis )

    Cos30=FPX/FP = 0.866 (FPX, X is the X axis )

    Here on there's supposed to be a way to Convert the above results to Newton Force.
    I dunno how to do that :S

    Anyway i need help with these, could someone help me ? :S
  2. jcsd
  3. Jan 12, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    To find the normal force, analyze the vertical components of the forces acting on the box. What must they add to?

    To find the acceleration, apply Newton's 2nd law in the horizontal direction. What's the net force on the box?
  4. Jan 12, 2008 #3
    the string applies force vertically and horizontally based on the angle. Use trig to find teh forces.
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