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Homework Help: Dynamics problems(force and friction and such)

  1. Mar 28, 2012 #1
    3 problems

    1. A 2.0 kg object is traveling at a constant speed of 1.4m/s[N] when it hits and ice patch. over the first 0.40m of the ice patch the object slows down to 0.85m/s[N]. what is coefficient of friction of the ice? (starting on a frictionless surface then slowing down)

    2. an object starts from rest and then travels 6.0m
    in 4.0s. if the coefficient of friction is 0.10 and there was an applied force of 9.0N
    , what was the mass of the object?

    3. Mr.Yahoo is pulling her friend's kids in a wagon with a force of 150N [E30*up] (which is equivalent to 130 N [E] and 75 N [up}. if the kids weigh 12kg, 8.0kg and the wagon weighs 3.0kg and the coefficient of friction is 0.43, what is their acceleration?

    Thank you in advance, please try to show full work and calculations and an idea of what a freebody diagram looks like.​
  2. jcsd
  3. Mar 28, 2012 #2


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    welcome to pf!

    hi thelegend123! welcome to pf :wink:

    show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:

    (start with 1.)
  4. Mar 28, 2012 #3
    Re: welcome to pf!

    i stated all of my variables

    i found the Fg = 19.6N and Fn = 19.6N i dont know where to go from here
  5. Mar 28, 2012 #4


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    do the geometry first, then the physics

    the geometry is to find the acceleration from the data

    then use physics to find the force, and then the coefficient of friction

    what do you get? :smile:
  6. Mar 28, 2012 #5
    not tosure on how to find accel?

    would it be using a kinematic equation v2^2 = v1^2 + 2ad

    but i don't think D has direction
  7. Mar 28, 2012 #6


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    that's right :smile:
    i don't understand :confused:

    (anyway, now i'm off to bed :zzz:)
  8. Mar 28, 2012 #7
    i got acceleration is -1.5ish and Fnet is 3.1N

    what now?
  9. Mar 28, 2012 #8
    Good. Your Fnet is equal to your friction force, right? What is your formula for finding the force of friction?
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