Which of the following pairs does not have same dimensions?
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:
The dimensional formula of Force is and for Time is .
Therefore, the dimensions of Impulse are:
- Momentum (linear momentum) is the product of mass and velocity:
The dimensional formula of Mass is and for Velocity is .
Therefore, the dimensions of Momentum are:
Since both have the dimensions , this pair has the same dimensions.
2. Moment of Inertia and Moment of Force:
- Moment of Inertia () is defined as the product of mass and the square of perpendicular distance:
Therefore, its dimensions are:
- Moment of Force (also known as Torque, ) is the cross product of position vector and force:
The dimensions of Force are and for Distance is .
Therefore, the dimensions of Moment of Force are:
Since , this pair does not have the same dimensions.
3. Angular Momentum and Planck's Constant:
- Angular Momentum () is defined as:
Its dimensions are:
- Planck's Constant () is derived from the relation , where is energy and is frequency:
The dimensions of Energy are and for Frequency are .
Therefore, the dimensions of Planck's Constant are:
Both have the same dimensions.
4. Work and Torque:
- Work is force times displacement:
- Torque is moment of force, which as calculated above has dimensions .
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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