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Basic physics units problems involving the Ideal Gas Law

  1. Sep 16, 2018 #1
    1. The problem statement, all variables and given/known data
    The following is the equation of ideal gas law, where p is pressure (Force/Area), V is volume, n is number of moles and T is temperature in Kelvin. What is the fundamental unit of R?
    pV = nRT
    A. kg^−1 · m^−2 · s^ 2 · K · mol
    B. kg^−1 · m^−4 · s ^2 · K · mol
    C. kg · m^4 · s ^−2 · K · mol^−1
    D. kg · m^2 · s ^−2 · K^−1 · mol^−1
    E. R is dimensionless

    The fundamental unit of acceleration a is ms^−2 . Which of the following equations is/are impossible? Give a brief justification. (t is time, v is velocity and A, B and C are dimensionless constants)
    A. a = A^−2BC^4 + v /t
    B. a = Cv /t
    C. a = v /t
    D. a = v/ t ^2
    E. a = t + v /t

    Which of the following is the typical mass (60 g) of a tennis ball?
    A. 6 × 10^4 mg
    B. 60 × 10^−1 kg
    C. 600 × 10^5 µg
    D. 6000 × 10^−5 g
    E. 60 000 × 10^5 ng
    2. Relevant equations

    3. The attempt at a solution
    I both calculated 60g in choice A and C
    but there should only be 1 answer in this q. idk what happened.

    2,1: cuz im a starter, i have no idea how things work in these 2 q.
    Last edited by a moderator: Sep 16, 2018
  2. jcsd
  3. Sep 16, 2018 #2


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    Your calculations in 3 are correct. Both A and C amount to 60 g.
    I cannot interpret this. Can you translate in plain English?
  4. Sep 16, 2018 #3
    sorry for my bad eng. in other words, i dont know how to calculate question 1 and 2.
  5. Sep 16, 2018 #4


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  6. Sep 16, 2018 #5
    in q2,choice B and C are possible. But im not sure if choiceA,D,E are possible or not
  7. Sep 16, 2018 #6


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    Staff: Mentor

    Can you state the reasoning you've used (so far) to reach the above conclusions?
    What rules of dimensional analysis have you invoked?
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