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Homework Help: Need help with 4 motion questions

  1. Sep 24, 2008 #1
    1. The problem statement, all variables and given/known data
    the teacher gave us 30 questions to do and i have no idea how to do these 4

    # A force of 1.6 N is applied to a box of mass 1.8 kg. It accelerates at 0.60 m/s2. Determine the force of friction that is acting and the coefficient of kinetic friction involved.

    # A desk of mass 45 kg is pushed across a rough surface (mK = 0.18) for a distance of 2.0 m by a constant force of 50 N. If the desk reaches a speed of 1.0 m/s by the end of the push, what was its speed at the beginning of the push? (Assume two significant digits.)

    A stationary elevator and its contents have a combined mass of 3000 kg. The elevator is suspended by a single cable. (Assume three significant digits.)

    1. Draw a free-body diagram of the elevator and calculate the values of all the forces that are acting on it when at rest.
    2. If the elevator is ascending at a speed of 3.0 m/s, what are the values of the forces acting at this point?
    3. If the elevator is descending at 3.0 m/s2, what are the values of all the forces acting at this point?

    # A ball is dropped over the side of a hot air balloon that is rising at 2.0 m/s. It strikes the ground 3.5 s later. Assume the only force acting on the ball is the force of gravity.

    1. From what height above the ground was the ball dropped?
    2. What is the balloon's altitude when the ball hits the ground?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 24, 2008 #2


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    Let's do them one at a time: what force is actually needed to give the box an acceleration of 0.60 m/s2?
  4. Sep 24, 2008 #3
    gravity..just don't know how to find the co efficent of friction
  5. Sep 25, 2008 #4


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    Draw a free body diagram. Indicate all the forces acting on the block. There should be at least four. Which forces balance out and what is the resultant force like?
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