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Homework Help: Centripetal Force and ball of string

  1. Nov 1, 2013 #1
    Hello, could someone look over my answer? I am not very confident I did the problem correctly.

    1. The problem statement, all variables and given/known data

    A 76-kg ball is tied to one end of a massless string of length The other end of the string is tied to a nail in the center of a table. The ball is set into uniform circular motion around the nail, and the tension in the string is 51 N. How long does the ball take to make one complete revolution? Assume friction with the table is negligible.
    A. 8.7 s
    B. 9.5 s
    C. 7.0 s
    D. 8.1 s

    2. Relevant equations

    T= m*a
    a = V^2/R
    V= 2*pi*R/T

    3. The attempt at a solution
    T = ma
    a = 51/76
    a= 0.67

    a= V^2/R
    V= √a*r
    V= √0.67*1.3
    V= 0.93

    V = 2*π*R/t
    t = 2*π*R/V
    t= 2*π*1.3/0.93
    t= 8.7 s
  2. jcsd
  3. Nov 1, 2013 #2

    T = mv^2/r
    51 = 76v^2/1.3
    v =.934

    ω = v/r
    ω = 0.934/1.3
    = 0.72

    0.72 = 2*∏*r/(r*t)
    t = (2*∏)/0.72
    = 8.7s

    Yes you were right.
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