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Particle In circular motion

  1. Jun 20, 2014 #1
    1. The problem statement, all variables and given/known data
    So I just sat an exam today and I'm not sure how I did in this question. I think I did bad in it.

    http://www.examinations.ie/archive/exampapers/2014/LC020GLP000EV.pdf [Broken]

    Its question 8


    2. Relevant equations
    F = mv^2/r

    v=ωr

    t=2(pi)r/v

    3. The attempt at a solution

    Q9

    (a)

    T=2(pi)r/v ....................... 0.4pi = 2pi(2)/v

    solving for v ............... 10 m/s

    v = rω

    10 = 2ω ................... ω = 5 rad/s

    a =v^2/r

    a = 10^2/2 = 50 m/s^2

    (i) 5 rad/s
    (ii) 10 m/s
    (iii) 50 m/s^2


    (B)

    (i) r = 1sin30 = 0.5m

    (ii) splitting its weight into components perpendicular and parallel to string

    parallel force = 2gcos30 = √3 g N

    Tension = parallel force
    Tension = √3 g N

    (iii) F = mv^2/r

    √3 g = 2v^2/.5
    solving for v = 2.06 m/s

    v = ωr

    2.06 = .5ω

    ω = 4.12 rad/s
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 20, 2014 #2

    BiGyElLoWhAt

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    Gold Member

    hmmm... well what exactly are you looking for? someone to check your work? If you're looking for that, the LEAST you can do is keep it all algebraic (symbolic) until the end. Too many numbers here.

    That being said, I didn't work through the first one, but ii) in solving for the tension, your setup is wrong, which means you probably got the wrong answer. What do you know about the vertical acceleration if it's constrained to moving along that circle? What is the value of that component?

    Now what else can you say that value is equal to?
     
  4. Jun 20, 2014 #3

    BiGyElLoWhAt

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    Gold Member

    also, you labeled it Q9, not Q8.
     
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