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Homework Help: Determining the Acceleration (Two objects in contact)

  1. Jan 8, 2015 #1
    1. The problem statement, all variables and given/known data
    2 crates, 75kg(crate x) and 110kg(crate z) are in contact and at rest on a horizontal surface. A 620N force is applied on crate x . If the coefficient of friction is 0.15, calculate:
    a.) the acceleration of the system
    b.)the force that each crate exerts on each other
    c.) repeat when the crates reversed

    2. Relevant equations

    Msys = (massx)+(massz)
    Force = mass(acceleration)

    3. The attempt at a solution

    a. Msys = 75kg + 110kg
    = 185kg
    620N = 185kg(a)
    a = 3.35m/s2

    cratex= 75kg(3.35m/s2)
    cratez= 110(3.35m/s2)

    cratez= 110(3.35m/s2)
    cratex= 75kg(3.35m/s2)

    thanks in advance!
  2. jcsd
  3. Jan 8, 2015 #2
    It may help to draw a force diagram to help yourself with this. For instance, with part A, you have to include friction as a part of what's going on with the system. So when you add up all the forces, you have a slightly different answer than what you have because the frictional force reduces the net force on the blocks in the direction of their displacement, and therefore reduces the acceleration. This is also what you have to keep in mind for parts B and C.
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