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Homework Help: Pushing force with friction

  1. Nov 10, 2014 #1
    I just want to check to see if I did the problem correctly.

    A person pushes a 2.0 kg box across a flat, horizontal surface with a force of 5.0 N for 4.0 m. Determine the acceleration of a box if the friction coefficient is 0.2.

    Determine the acceleration of the box if the friction coefficient is 0.2.

    First, we need to find the static force.
    [tex] F_s= \mu F_n = (0.2) (2 \cdot 9.81) = 3.924 \ N [/tex]

    Then, we need to find the net force.
    [tex] F_{net} = 5 \ N - 3.924 \ N = 1.076 \ N[/tex]

    Then, finally, the acceleration of the box is:
    [tex] F=ma \Rightarrow 1.076 = (2 \ kg) \ a \Rightarrow \boxed{a=0.538 m/s^2}[/tex]

    Is that right? Any help is appreciated.
  2. jcsd
  3. Nov 11, 2014 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    The 5N force was horizontal?
    Than that was just about perfect.

    It is best practice to do the algebra before putting the numbers in.
    So: From Newton's second law: $$F+\mu mg = ma \implies a=\frac{F+\mu mg}{m}$$... F=5N, ##\mu##=0.2, and m=2kg;$$a=0.538\text{m/s}^2$$
  4. Nov 11, 2014 #3

    Thanks so much! :)

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