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Forces Acting On Two Blocks : mostly conceptual

  1. Feb 19, 2008 #1
    1. The problem statement, all variables and given/known data
    Block A is on top of Block B, which is on a frictionless incline. The mass of Block A is less than that of Block B. The positive x-direction is defined to be up the ramp.

    During the interval from t1 to t2 a hand exerts a constant force on block A in the positive x-direction. Both blocks move a distance d in positive x-direction and speed up. The blocks do not slip relative to each other, as show in the diagrams below

    Image is attatched


    consider an instant during the interval from t1 to t2

    a) is the magnitude of net force on block A greater than, less than, or equal to the magnitude of the net force on block B

    b) Draw 2 separate free-body diagrams, one for each block. Label each force with 1)type of force 2) the object on which the force is exerted 3) the object exerting the force

    c) Rank the magnitudes of all the forces in your free-body diagrams that are parallel to the ramp( so only the ones that point entirely to the positive or negative x-direction

    Last one I promise

    d) Write newton's second law for block A only. Include all the info about the magnitude and the direction of the forces exerted on block A, as well as the direction of the acceleration of Block A.

    2. Relevant equations
    Since these are mostly concept questions im going to guess there aren't any. Correct me if I'm wrong.


    3. The attempt at a solution

    a) The magnitude of the net force on block A is EQUAL TO the magnitude of the net force on block B. I put this answer because the question states that the blocks don't slip relative to each other and from t1 to t2 their net forces are going pointing in the same direction.

    b) I'm just going to list the forces instead of drawing it and uploading it. Block A: Gravity, Normal Force, Force of the push, Static Friction between blocks A and B. Block B Gravity, Normal Force, Force of push?, friction between the floor and block b

    c)block A: static friction between block A and B, force of push
    block B: force of push, friction between the floor and block b

    d) I don't know how to answer this question but i do know that newton's second law describes the behavior of objects when all existing forces are not balanced. I'm not sure what the question is asking me to do.



    THANKS! ahead of time
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Feb 19, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Since they move together, their acceleration must be the same. But what about their mass?

    OK.
    (1) The push is on block A, not block B; (2) How many normal forces act?; (3) Where's the friction? (The incline is frictionless.)

    Redo this in light of the above comments. And rank order them.

    Just take a shot.
     
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