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Homework Help: Newton's Laws Applications - Systems

  1. Nov 5, 2013 #1

    I am taking intro Physics and we are having a little quiz this friday. Professor gave us handouts and told us to solve them by ourselves, and then study those problems because the same problems will be on the quiz. Now, my problem is, is that I really don't understand the subject, because professor just gives us these handouts and expects us to solve them by ourselves after a one minute quick explanation.

    This handout has 12 problems, I know how to draw labels on them and do a free-body diagram... but I don't know how to do calculations... professor didn't help us do them, so I'm trapped in a paradox, I want to study for friday but have no material to study from. So, can you help me solve the CALCULATIONS (I know how to draw labels), so I can study and examine them by friday and not fail the quiz?

    Since they are graphs and I can't draw here, I attached 5 well-visible images.

    1st: http://img28.imageshack.us/img28/5849/nggw.jpg [Broken]
    2nd: http://img5.imageshack.us/img5/6608/81oz.jpg [Broken]
    3rd: http://img14.imageshack.us/img14/7445/xcup.jpg [Broken]
    4th: http://img30.imageshack.us/img30/5777/13x.JPG [Broken]
    5th: http://img35.imageshack.us/img35/8440/2uk.JPG [Broken]

    Here are my attempts but there's no chance they're correct:

    1st: http://img849.imageshack.us/img849/6103/pxcq.jpg [Broken]
    2nd: http://img543.imageshack.us/img543/686/4r6u.jpg [Broken]
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Nov 5, 2013 #2

    Andrew Mason

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    For the first problem, is there any difference between the magnitude of the tension acting on m and of the tension acting on M?

    How is the acceleration of M related to the acceleration of m?

    Can you write the equations for the accelerations of m and M and for the relationship between their accelerations? That should give you 3 equations and 3 unknowns (am, aM, and T) which you can now solve.

    Last edited by a moderator: May 6, 2017
  4. Nov 5, 2013 #3
    No, there's no difference between the magnitude of the tension in problem 1.

    As for the acceleration, in those problems, we are supposed to find:
    normal force

    Masses will be given, as well as coefficient of friction (only kinetic friction).

    As for equations, that's where I have a problem, I'm trying to have examples so I can then study those examples and solve new problems.
  5. Nov 6, 2013 #4

    Andrew Mason

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    I'll give you the first equation.

    From free-body diagram, add the force vectors to find the net force:

    [itex]\vec{F_M} = M\vec{g} + \vec{T} = M\vec{a_M}[/itex]

    Since the net force is down, letting down be positive, the force magnitudes add this way:

    [itex]F_M = Mg - T = Ma_M[/itex]

    Can you write the similar equation for m? Then relate the two accelerations.

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