# Basic physics units problems involving the Ideal Gas Law

## Homework Statement

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

## The Attempt at a Solution

3:
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:

kuruman
Homework Helper
Gold Member
2021 Award
Your calculations in 3 are correct. Both A and C amount to 60 g.
2,1: cuz im a starter, i have no idea how things work in these 2 q.
I cannot interpret this. Can you translate in plain English?

Your calculations in 3 are correct. Both A and C amount to 60 g.

I cannot interpret this. Can you translate in plain English?
sorry for my bad eng. in other words, i dont know how to calculate question 1 and 2.

kuruman
Homework Helper
Gold Member
2021 Award
Are you familiar with dimensional analysis? Most textbooks deal with it in chapter 1. Read your textbook about it and see here for another example
https://www.physics.uoguelph.ca/tutorials/dimanaly/

in q2,choice B and C are possible. But im not sure if choiceA,D,E are possible or not

gneill
Mentor
in q2,choice B and C are possible. But im not sure if choiceA,D,E are possible or not
Can you state the reasoning you've used (so far) to reach the above conclusions?
What rules of dimensional analysis have you invoked?