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Easy N2L question grade 11 physics

  1. Nov 14, 2011 #1
    Easy N2L question.... grade 11 physics

    Problem: A 500g dynamics cart is attached to a 50g mass, which is suspended over a pulley. When released from rest, it took 1.5 s for the cart to move a distance of 1m.

    Find: a) acceleration of cart,
    b) friction between cart and track




    Attempt; a) Given: Δd=1m, Δt=1.5s

    Δv= Δd/Δt
    Δv=1/1.5
    Δv=.666 m/s

    a=Δv/Δt
    a=.666/1.5
    a=.444 m/s²

    Thus, ave. acceleration of cart = .444 m/s²

    b) Given: Fapp = 0.49 N, mcart=.500 kg, a=.444 m/s²

    FNet= ma → (.5)(.444)
    FNet= .222

    FNet= Fapp + f + FN + Fg (FN & Fg are redundant)

    .222= 0.49 + f → .222 - .49 = f
    f= -.268 N

    Therefore friction = .268 N
     
  2. jcsd
  3. Nov 14, 2011 #2

    PeterO

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    Re: Easy N2L question.... grade 11 physics

    The line in red is incorrect. average velocity = Δd/Δt

    When the object starts at rest, and has constant acceleration, the final velocity is twice the average velocity.
     
  4. Nov 14, 2011 #3

    SammyS

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    Re: Easy N2L question.... grade 11 physics

    See comments above.

    The total amount of mass being accelerated is 550 g.
     
  5. Nov 14, 2011 #4
    Re: Easy N2L question.... grade 11 physics

    Attempt; a) Given: Δd=1m, Δt=1.5s

    Δv= Δd/Δt
    Δv=1/1.5
    Δv=.666 m/s

    a=Δv/Δt
    a=(.666/1.5) x 2
    a=..888 m/s²

    Thus, acceleration of cart = .888 m/s²

    b) Given: Fapp = 0.49 N, mcart=.550 kg, a=.888 m/s²

    FNet= ma → (.550)(.888)
    FNet= .4882

    FNet= Fapp + f + FN + Fg (FN & Fg are redundant)

    .4882= 0.49 + f → .4882 - .49 = f
    f= -.0016?

    Therefore friction = .0016 N
     
  6. Nov 15, 2011 #5

    PeterO

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    Re: Easy N2L question.... grade 11 physics

    There is a chance this final answer is correct - but the explanations are very confused and contradictory.
     
  7. Nov 15, 2011 #6
    Re: Easy N2L question.... grade 11 physics

    Above poster SammyS said total mass was 550g, so I would assume to use 550g as my total mass for finding FNet right? I will fix the question when I write it out to make it more comprehensible!
     
  8. Nov 15, 2011 #7

    PeterO

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    Re: Easy N2L question.... grade 11 physics

    You may well be correct to use 550g, but you still call it mcart !! That's the problem.
     
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