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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Introduction to Physics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Introduction to Physics

Determine if the following equation is dimensionally correct: v =...

Determine if the following equation is dimensionally correct:
v=Pρv = \sqrt{\dfrac{P}{\rho}}
where h=h = height, S=S = surface tension, ρ=\rho = density, P=P = pressure, V=V = volume, η=\eta = coefficient of viscosity, ν=\nu = frequency and I=I = moment of inertia.

Options

  1. AThe equation is dimensionally incorrect, as the right side has dimensions of [LT−2][L T^{-2}].
  2. BThe equation is dimensionally incorrect, as the right side has dimensions of [L2T−2][L^2 T^{-2}].
  3. CThe equation is dimensionally incorrect, as the right side has dimensions of [MLT−1][M L T^{-1}].
  4. DThe equation is dimensionally correct.

Correct answer

D. The equation is dimensionally correct.

Step-by-step solution

The dimensions of the left-hand side (velocity, vv) are:
[v]=[LT−1][v] = [L T^{-1}]

The dimensions of the terms on the right-hand side are:
Pressure, P=ForceArea=[MLT−2][L2]=[ML−1T−2]P = \dfrac{\text{Force}}{\text{Area}} = \dfrac{[M L T^{-2}]}{[L^2]} = [M L^{-1} T^{-2}]
Density, ρ=MassVolume=[M][L3]=[ML−3]\rho = \dfrac{\text{Mass}}{\text{Volume}} = \dfrac{[M]}{[L^3]} = [M L^{-3}]

Substituting these into the right-hand side expression:
Pρ=[ML−1T−2][ML−3]=[L2T−2]=[LT−1]\sqrt{\dfrac{P}{\rho}} = \sqrt{\dfrac{[M L^{-1} T^{-2}]}{[M L^{-3}]}} = \sqrt{[L^2 T^{-2}]} = [L T^{-1}]

Since the dimensions of the left-hand side are equal to the dimensions of the right-hand side, the equation is dimensionally correct.
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