Question Details

Which of the following pairs does not have same dimensions?

Options

A

impulse and momentum

B

moment of inertia and moment of force

C

angular momentum and Planck's constant

D

work and torque

Correct Answer :

moment of inertia and moment of force

Solution :

To determine which of the given pairs does not have the same dimensions, let's analyze the dimensions of each quantity in each option one by one.

1. Impulse and Momentum:
- Impulse is defined as the product of force and time:
Impulse=Force×Time
The dimensional formula of Force is [MLT-2] and for Time is [T].
Therefore, the dimensions of Impulse are:
[MLT-2]×[T]=[MLT-1]
- Momentum (linear momentum) is the product of mass and velocity:
Momentum=Mass×Velocity
The dimensional formula of Mass is [M] and for Velocity is [LT-1].
Therefore, the dimensions of Momentum are:
[M]×[LT-1]=[MLT-1]
Since both have the dimensions [MLT-1], this pair has the same dimensions.

2. Moment of Inertia and Moment of Force:
- Moment of Inertia (I) is defined as the product of mass and the square of perpendicular distance:
Moment of Inertia=Mass×Distance2
Therefore, its dimensions are:
[M]×[L2]=[ML2]
- Moment of Force (also known as Torque, τ) is the cross product of position vector and force:
Moment of Force=Force×Distance
The dimensions of Force are [MLT-2] and for Distance is [L].
Therefore, the dimensions of Moment of Force are:
[MLT-2]×[L]=[ML2T-2]
Since [ML2][ML2T-2], this pair does not have the same dimensions.

3. Angular Momentum and Planck's Constant:
- Angular Momentum (L) is defined as:
L=r×p=Distance×Linear Momentum
Its dimensions are:
[L]×[MLT-1]=[ML2T-1]
- Planck's Constant (h) is derived from the relation E=hν, where E is energy and ν is frequency:
h=EnergyFrequency
The dimensions of Energy are [ML2T-2] and for Frequency are [T-1].
Therefore, the dimensions of Planck's Constant are:
[ML2T-2][T-1]=[ML2T-1]
Both have the same dimensions.

4. Work and Torque:
- Work is force times displacement:
Work=Force×Displacement=[MLT-2]×[L]=[ML2T-2]
- Torque is moment of force, which as calculated above has dimensions [ML2T-2].
Both have the same dimensions.

Thus, the only pair that does not share the same dimensions is moment of inertia and moment of force.

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