Question

Which of the following is different from others?
A. Mass
B. Length
C. Time
D. Density

Answer 1

Hint: In the given options, one of the physical quantities is a derived quantity and rest of the quantities is fundamental quantities. Fundamental quantities are independent of other physical quantities while derived quantities are derived from two or more fundamental quantities. Other examples of fundamental quantities are temperature, current, etc.

Complete answer:
To answer this question, let us understand what are fundamental quantities and derived quantities.
Fundamental quantities: We can define fundamental quantities as the physical quantities which are independent of other physical quantities. The fundamental quantities usually have the single unit like meter, mass and second, etc.
Derived quantities: We can define derived quantities as the physical quantities which are derived from two or more fundamental quantities. For example: force, acceleration, work, frequency, etc.

As we know the mass is not derived from other physical quantities. Its unit is kilograms. Therefore, the mass is the fundamental quantity.Length is also not derived from other physical quantities. Its unit is only meters. Therefore, the length is the fundamental quantities. Time is also not derived from other physical quantities. The unit is second. Therefore, time is the fundamental quantity.Now, we know that the density is the ratio of mass to the volume of an object. Thus, the density is derived from two fundamental quantities. The unit of density is kilogram per cubic meter. Therefore, the density is not a fundamental quantity.

So, the correct answer is option D.

Note:Students must note that however the quantities like force, energy, etc have the single unit that is newton and joule, these units are also known as derived units. Newton is the S.I unit of force and the force is the product of mass and acceleration. The energy has the unit of newton-meter.