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Homework Help: Two physics questions

  1. Nov 8, 2007 #1
    1. The problem statement, all variables and given/known data

    Which of the following is not a unit of velocity?
    A) m/s C) km/ms
    B) m/N D) mm/ms

    If an object starts from rest and travels a distance d in t sec, which of the following equations may be used to find its acceleration?
    A) Vf = Vi + at C) d = Vi t + ½ at2
    B) Vf2 = Vi2 +2ad D) d = ½ (Vf + Vi) t

    2. Relevant equations

    In problems

    3. The attempt at a solution
    Ok, for #1 I am going or answer B because I have never seen that before.

    FOr the 2nd one, I amgoing to go with A.

    AmI right?
  2. jcsd
  3. Nov 8, 2007 #2
    Only A is a unit of velocity.

  4. Nov 8, 2007 #3

    Shooting Star

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    Homework Helper

    Use some logic.

    1. Velocity has dimension of distance/time. Which of them does not ultimately decompose into that?

    2. Choice A doesn't even have 'd' in it. Which one has d and t and the initial velocity?
  5. Nov 8, 2007 #4
    kilometers per millisecond and mmillimeters per millisecond may be very unusual units of velocity (more properly speed since direction is unstated) but they are units of speed.
  6. Nov 8, 2007 #5
    Damn, im sorry.


    So #1 is B

    and # 2 is C

  7. Nov 8, 2007 #6

    Shooting Star

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    That's more like it!
  8. Nov 8, 2007 #7
    C. Using one of the three laws of projectile motion.

    It obviously cant be A as it doesn't have Distance in it. It can't be B because that doesn't have time in it and D doesn't even hold acceleration.

    Therefore C is the right answer you would just need to re-arrange the equation to get a as a subject.
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