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Homework Help: Applying newtons laws n an inclined surface with two masses

  1. Mar 19, 2009 #1
    applying newtons laws on an inclined surface with two masses

    1. The problem statement, all variables and given/known data
    Two blocks connected by a cord passing over a small, frictionless pulley rest on frictionless planes (diagram attached)
    a) which way will the system move when the blocks are released from rest?
    b) what is the acceleration of the blocks?
    what is the tension in the cord

    2. Relevant equations
    Newtons laws

    3. The attempt at a solution
    i have not gotten very far in this question as i keep going around in circles, actually i am finding this whole topic difficult but this is my attempt

    a) find the force each block the largest force determines which way it will slide

    w1 =mg
    =100 x 9.8
    w2 =50 x 9.8
    = 490
    in component form
    x1 = wsin30 y1 = wcos30
    y2 = wsin53 y2 = wcos53

    but this is where i get stuck
    im not sure if i need to take into the block attached at the other end or take each side of the triangle in isolation

    i hope you understand cause im not sure if i am making any sense
    thanks in advanced

    Attached Files:

    Last edited: Mar 19, 2009
  2. jcsd
  3. Mar 19, 2009 #2
    Which is greater?
    100 g sin 30 or
    50 g sin 53.
    Direction of motion depends on that. You don't have to account frictional forces in this case, since its given that the planes are frictionless.
  4. Mar 19, 2009 #3
    thanks for that so the system moves to the right
    to do part b)
    is the x component of acceleration equal to (980sin30+490sin53)/150
    which equals 5.88
    then you do a similar thing for the y component using the cos values
    then to work out the total acceleration you use Pythagorean therm
    resulting in 9.625
    is this the correct method of working
  5. Mar 19, 2009 #4
    Why use the Pythagorean theorem to find out the total acceleration? :confused:
    There is no frictional force acting on either of the two blocks. Which component of weight causes the body to accelerate?
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