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41.(AIEEE 2005 )

Out of the following pair, which one does NOT have identical dimensions is

(A) angular momentum and Planck's constant

(B) impulse and momentum

(C) moment of inertia and moment of a force

(D) work and torque

Correct answer is (C)

Moment of inertia, I = Mr2

[I] = [ML2]

Moment of force, τ = r × F

[ τ ] = [ L ] [ M L T 2 ] = [ M L 2 T 2 ]

42.(AIEEE 2004 )

Which one of the following represents the correct dimensions of the coefficient of viscosity?

(A) ML-1T-1

(B) MLT-1

(C) ML-1T-2

(D) ML-2T-2

Correct answer is (A)

From stokes law, Viscous force F = 6 π η r v

η = F 6 π r v

[ η ] = [ M L T 2 ] [ L ] [ L T 1 ]

[ η ] = [ M L 1 T 1 ]

43.(AIEEE 2003 )

Dimensions of 1 μ 0 ε 0 , where symbols have their usual meaning, are

(A) [ L-1T ]

(B) [ L-2T2 ]

(C) [ L2T-2 ]

(D) [ LT-1 ]

Correct answer is (C)

The velocity of light in vacuum is

c = 1 μ 0 ε 0 ;

[ 1 μ 0 ε 0 ] = [c2] = [L2T-2]

Dimension of 1 μ 0 ε 0 = [L2T-2]

44.(AIEEE 2003 )

The physical quantities not having same dimensions are

(A) torque and work

(B) momentum and Planck's constant

(C) stress and Young's modulus

(D) speed and ( μ 0 ε 0 ) 1 / 2

Correct answer is (B)

Momentum = mv = [ M L T 1 ]

Planck's constant, h = E v = [ M L 2 T 2 ] [ T 1 ] = [ M L 2 T 1 ]

So Momentum and Planck's constant do not have same dimensions.

45.(AIEEE 2002 )

Identify the pair whose dimensions are equal

(A) torque and work

(B) stress and energy

(C) force and stress

(D) force and work

Correct answer is (A)

Work (W) = F . s = Fs cos θ

= [MLT-2][L] = [ML2T-2];

Torque ( τ ) = r × F τ = r F sin θ

= [L] [MLT-2] = [ML2T-2]

So dimension of torque and work are same.