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Homework Help: Dynamics problem

  1. May 2, 2006 #1
    Hello, i'm a high school physics student and i have trouble solving this dynamics problem related to tension and stuff... heres the question

    3 blocks of masses 10kg, 5kg and 3kg are connected by a light string that pass over a frictionless pulley as shown. the acceleration of the 5kg block is 2ms^-2 to the left, and the surfaces are rough. find (a) the tension in each string and (b) the coefficient of the kinetic friction between the blocks and the surfaces.

    The diagram is attached to my post. I drew a rough one in paint.

    Please help me guys! I've got to hand in this assignment tomorrow and i cant do this question =(.

    Attached Files:

  2. jcsd
  3. May 2, 2006 #2


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    Equate the forces in the horizontal and vertical directions...

    Think which force is acting in which direction, eg. the weight on the left only has a vertical component downwards...
  4. May 2, 2006 #3


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    Staff: Mentor

    Start out by labelling what you do know from the problem statement onto the diagram. You know the force of gravity on the outer two blocks, and you know the initial velocities of the blocks, right? What are the frictional forces on the two righthand blocks? Gravity, friction and string tension are the only forces acting on the blocks, right?
  5. May 2, 2006 #4
    Thanks for the explanations but i still dont quite get it... Could i ask for more detailed help?
  6. May 2, 2006 #5


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  7. May 5, 2006 #6
    Just remember, you need three things. First is an understanding of Newton's laws, which help in organizing the math needed to solve the problem. Second, be ery clear with your labeling of your variables and yor axes. You can call them whatever you want and give anydirection the positive or negative choice, but once you choose, BE CONSISTENT WITH IT or your answer might turn out to be something different. And finally, take care with your trig, fractions, algebra and all that jazz.
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