Physics Units, Dimensions and Measurement NTA Abhiyas Question - Units and Dimensions MCQ (Single Correct)

If velocity, force and time are taken as the fundamental quantities, then using dimensional analysis choose the correct dimensional formula for mass among the following. [K is a dimensionless constant]

A
Q = K v -l FT
B
Q = K v 3 F T 2
C
Q = 2 K v -l F T
D
Q = 3 K v 2 F T

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Text Solution

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The correct answer is:
A

Q = K v -l F T

Let the quantity be Q, then,

Q = f(v,F,T)

Assuming that the function is the product of power functions of v, F and T,

Q = Kv x F y T z ... (i)

where K is a dimensionless constant of proportionality. The above equation dimensionally becomes

[Q] = [LT -1 ] x [MLT -2 ] y [T] z

i.e., [Q] = [M y L (x+y) T (-x-2y+z) ],Now

Q = mass i.e., [Q] = [M]

So Equation (ii) becomes

[M] = [M y +L (x+y) T (-x-2y+z) ]

its dimensional correctness requires

y = 1, x + y = 0 and - x - 2y + z = 0

which on solving yields

x = - 1, y = 1 and z = 1

Substituting it in Equation (i), we get

Q =Kv -1 FT

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