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Homework Help: Frozen pond friction problem

  1. Dec 6, 2009 #1
    1. The problem statement, all variables and given/known data

    A 680 N student stands in the middle of a frozen pond having a radius of 6.0 m. He is unable to get to the other side because of a lack of friction between his shoes and the ice. To overcome this difficulty, he throws his 2.6 kg physics textbook horizontally toward the north shore at a speed of 10.0 m/s. How long does it take him to reach the south shore?

    2. Relevant equations



    3. The attempt at a solution

  2. jcsd
  3. Dec 6, 2009 #2
    Re: Momentum

    Please at least attempt a solution next time. I'll help you out anyway because I'm bored.

    The basic strategy behind solving this problem centers on conservation of momentum. Before we get to that, however, we need to find out the mass of the student. We know the student's weight, W, and from that we can figure out the mass:

    [tex] W = m_sg[/tex]

    >> [tex]680 N = m_sg[/tex]

    >> [tex]m_s = 69.4 kg[/tex]

    With that out of the way, we can use conservation of momentum:

    [tex] P_i = P_f[/tex]

    >> [tex] m_bv_b + m_sv_s = m_bv_b + m_sv_s [/tex]

    The left side of the equation is 0. There is no initial momentum. The book and the person are both at rest. This leaves us with the following equation:

    [tex] 0 = m_bv_b + m_sv_s[/tex]

    Plug everything in and solve for the velocity of the student:

    [tex]v_s = -.37 m/s[/tex]

    Now it's simple kinematics:

    [tex] distance = velocity * time[/tex]

    Solve for time:

    [tex]t = 16 seconds[/tex]
  4. Dec 6, 2009 #3
    Re: Momentum

    I apologize I had attemped it myself i just didn't want to write something completely wrong on here i thought it would just complicate things. Will do next time though.

    Thank you for the help I appreciate it. Very easy to follow.

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