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Calculating the distance of a sliding block

  1. Dec 18, 2005 #1
    1) I would like to know if I found the deceleration correctly.
    Since the force of friction is coefficient of friction * Normal Force, and F = ma, would the deceleration be force of friction/mass?

    2) How do I calculate the total distance a sliding block traveled? (The block was pushed.)
     
  2. jcsd
  3. Dec 18, 2005 #2

    Doc Al

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    If friction is the only force accelerating the block (for example, the block has a initial speed on a horizontal surface), then Newton's law tells you that a = F/m. Now if you use what you know about the friction force, what's the resulting acceleration? (What's the normal force?)
    Several ways: (1) Using the kinematic relationships for uniformly accelerated motion, or (2) using energy methods.
     
  4. Dec 18, 2005 #3
    The resulting acceleration would be the applied force plus the force of friction. Since the force of friction is opposing force to the applied force, it's basically subtracting the two values. Normal force is the positive value of the object's weight.

    Which energy formulas would I use? Can you steer me in the right direction?
     
  5. Dec 18, 2005 #4

    Doc Al

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    I'm a bit confused about the problem. Is there an applied force in addition to the friction? If that force exceeds the friction force, why would the block slow down?

    In any case, the acceleration would equal the net force divided by the mass.

    OK.
    Again, please describe the problem exactly as it was given, so I don't steer you wrong.

    If it's just a block being slowed by friction, the work done by friction in bringing it to a complete stop must equal (in magnitude) the initial kinetic energy of the block.
     
  6. Dec 18, 2005 #5
    I'm writing a program and I need to know the pushed block's final distance. The user will input the amount of the applied force. I just have it so that the block is pushed for a second and it'll slide after that point. After it's been given a push, it'll have so-and-so speed and acceleration - and since the block is not on a frictionless surface, it is bound to slow down.
     
  7. Dec 18, 2005 #6

    Doc Al

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    OK, much clearer. You'll need to break this into two pieces:

    (1) While the push is being applied, there are two forces acting. Find the net force and thus the acceleration. Find the block's speed after one second (assuming it starts from rest).

    (2) Once the push is removed, the only force is the friction. Find the new acceleration (or de-acceleration, if you prefer). You have the initial speed (from part 1), now find the distance it slides using kinematics (or by calculating the work done by friction).
     
  8. Apr 3, 2006 #7
    really need help now now now please

    hi
    i have a few questions to ask.

    firstly, i'm trying to calculate F(mu) and Fn using the F(mu)=Fg sin(theta) and Fn=Fg cos (theta) for the object and shoe for both the initial and added weight. THe angle is 37.7 degree's for object 1 and with weight is 42 degrees and the 2nd one is 40.3 degrees for object 2 and weight is 41.3 degrees.
    also am having trouble determining things on excel but can someone add me to their msn and i'll explain further.
    thanks heaps!
    olivia
     
  9. Apr 3, 2006 #8
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