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Newton's second law problem;

  1. Sep 30, 2009 #1
    Newton's second law problem; Please Help!

    Block M = 7.50 kg is initially moving up the incline and is increasing speed with
    a = 4.35 m/s2. The applied force F is horizontal. The coefficients of friction
    between the block and incline are fs = 0:443 and fk = 0:312. The angle of the incline is
    25.0 degrees.
    (a) What is the force F?

    So basically, I started by tilting the axes. Then, I did F=ma. I plugged 7.5 kg into m and 4.35 into a. I got 32.6 N. Then, I took 32.6/cos(25) to get the horizontal component of force. My answer was 35.99 N. It says that my answer should be around 80 N to 120 N. What did I do wrong? Please Help.
  2. jcsd
  3. Oct 1, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Re: Newton's second law problem; Please Help!

    To apply Newton's 2nd law you must consider all the forces. What other forces act parallel to the incline?

    Hint: You'll need to analyze both vertical and horizontal force components.
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