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Homework Help: Newton's Second Law

  1. Oct 12, 2008 #1
    1. The problem statement, all variables and given/known data

    I have attempted a (bad) drawing of the problem below.

    FA=100 N
    M1=20 kg
    M2=30 kg
    Theta=30 degrees
    g=10 m/s2

    The black stuff in the photo are what we were given. Red is what I added, but some things are missing and I'm not sure on others. I am not sure on any of the forces on M3 besides T and mg. Also, I'm not sure if M2 has an acceleration force as well.

    1. Normal force acting on M1
    2. Normal force acting on M2
    3. Force of friction acting on M1
    4. Force of friction acting on M2
    5. Direction M3 moves
    6. Net force acting on the system
    7. Acceleration of the system
    8. Net force acting on M1
    9. Net force acting on M2
    10. Net force acting on M3
    11. Tension in string A
    12. Tension in string B

    2. Relevant equations


    3. The attempt at a solution

    1. Fsin(theta)+n=0
    n=(20 kg)(10 m/s2)-(100 N)sin(30)

    2. mgcos(theta)-n=0
    n=(30 kg)(10 m/s2)cos(30)

    3. fk=ukn

    4. fk=ukn

    5. Down? I feel like there should be more to this one.

    6. This is where I get stuck. I started out writing Fnet=ma, Fcos(theta)=ma, and from there I got lost. When I do this do I do a net force in the X and Y directions separately, or am I missing a formula somewhere?

    7-12. As far as I know, I will need the answer to 6 before I can get any of these, so if I get some help on this one I will try to do the rest and post my results here.

    Thanks to anyone who is taking the time to try to help me!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
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