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Friction Problem -- String, Block, Bucket & Washers

  1. Nov 19, 2014 #1
    1. The problem statement, all variables and given/known data
    A string is tied to a 4.4 kg block and 120g hanging bucket. Students add 20g washers one at a time to the bucket. The student are unaware that the
    coefficient of static friction for the block on the table is 0.42.
    A) what is the maximum force of static friction for the block?
    Answer: 18.11N
    B) how many washers can the students add to the bucket without moving the block?
    Answer: 86
    C) the coefficient on kinetic friction is 0.34. Calculate the acceleration of the block when the final washer is added to the bucket and the objects start to move...

    The diagram is the block on table with the pulley on the edge of the table holding the bucket vertically. They are tied with one string.
    How do get c)? I got 0.56m/s^2 but the answer in the book is 0.75m/s^2

    2. Relevant equations
    a= m2g -Fs/ m1 + m2

    3. The attempt at a solution
    a= m2g -Fs/ m1 + m2
    a= (1.86 x 9.8) - 15/ (4.4 + 1.86)
    a= 0.52m/s^2
    I got Fs by...
    Fs = (0.34)(Fn=4.4x9.8)
    = 1.86
    I got m2 by...
    1. calculating the mass of the washers
    20g x 87 washers = 1740g
    2. adding the bucket and washers
    120g + 1740g = 1860g
    3. converted to kg
    1860g/1000g=1.86 kg
     
  2. jcsd
  3. Nov 19, 2014 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You got 0.56 but in 3) you use 15 instead of 14.66 and mention 0.52 m/s2. Confusing.

    Nevertheless, I get 0.57 and suspect a typo in the book answer
     
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