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Homework Help: Distance travelled during acceleration.

  1. Aug 26, 2009 #1
    1. The problem statement, all variables and given/known data

    A cyclist accelerates from rest to a velocity of 3 m/s in 12 seconds, continues at this speed for one minute and then freewheels to stop. If the total mass of cyclist and cycle is 80 kg, and the tractive resistance rate may be assumed constant at 0.2 N/kg.,

    2. Relevant equations
    s= 1/2(u+v)t

    3. The attempt at a solution

    my attempt was

    s= 1/2(0+3)12
    s= 72

    im not too sure if that's right but i tryed my best :)
  2. jcsd
  3. Aug 26, 2009 #2
    How did you get from s=1/2(3)12 to s=6x12?
  4. Aug 26, 2009 #3
    my bad s= 1/2(u+v)t
    s= 1/2(0+3)12
    s= 1/2(3)12
    s= 1.5(12)
    s= 18m

    Work done during acceleration and constant velocity

    w= 36x18
    w= 648 joules

    now how to find the constant velocity?

    is it

    c.v => (Mass x Tractive resistance rate)
    c.v= 80x0.2
    c.v= 16N ?
  5. Aug 26, 2009 #4
    Hm...what exactly are you trying to calculate from the scenario (what's the question asking for?)
    16N is the tractive resistance force (ie. friction). Where does this constant velocity thingy come from?
  6. Aug 26, 2009 #5
    second part of the question.
  7. Aug 26, 2009 #6
    Is it just me or is the question spliced off after "...assumed constant at 0.2 N/kg.,"? Cos' from the the spliced extract, I only see a scenario and no questions.
  8. Aug 26, 2009 #7
    Is the Distance travelled during acceleration correct?

    The constant velocity come from the second part of question (iii).

    (iii)Determine The work done during acceleration and the constant velocity.

    Work done during acceleration

    w= 36x18
    w= 648 joules

    now how to find the constant velocity?

    my try was.

    c.v => (Mass x Tractive resistance rate)
    c.v= 80x0.2
    c.v= 16N ?
  9. Aug 26, 2009 #8
    The constant velocity is, as given in the question, 3m/s.
    Work done during this period is then simply the frictional force X displacement since forward driving force = frictional force (magnitude)
  10. Aug 26, 2009 #9
    if the constant velocity is, as given 3m/s. why do they ask me to find the constant velocity?
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