Tag: fundamental and derived units

Questions Related to fundamental and derived units

The effect of an impulse force on the body is measured only in terms of its

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. Force

  2. Moment of momentum

  3. Impulse

  4. None of these

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Correct Option: C
Explanation:

The effect of an impulse force on the body is measured only in terms of impulse. If a moving object is stopped by an impact, the change in momentum of the object occurs. This change in momentum is called the impulse.

Energy cannot be measured in

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. $Js$

  2. $Ws$

  3. $kWh$

  4. $erg$

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Correct Option: A
Explanation:

$W \ s$, $kWh$ and $erg$ are the unit of energy but $J \ s$ is not the unit of energy. So, energy cannot be measured in $J \ s$

$ \dfrac{kg}{m^3} $ is an  S.I unit of density.

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. True

  2. False

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Correct Option: A
Explanation:

The density of a body is defined as the ratio of the mass to the volume of the body.

The SI unit of density is $\dfrac { Kg }{ { m }^{ 3 } } $.

SI unit of momentum is

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. $dyne \cdot sec$

  2. $g\cdot cms^{-1}$

  3. $Ns$

  4. $gm\cdot s$

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Correct Option: C
Explanation:

Momentum $=$ mass X velocity  $=kg\dfrac { meter }{ { sec } } $

                    $ =$ force X time $=$ newton. second

Any unit which can be obtained by the combination of one or more fundamental units is called

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. Fundamental unit

  2. Scale

  3. Derived unit

  4. Standard unit

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Correct Option: C
Explanation:

The units which can neither derived from one another nor resolved into any thing more basic are called fundamental unit. It is independent of any other unit. Any unit which can be obtained by the combination of one or more fundamental units is called derived unit.

Unit of relative density is $kg\ m^{-3}$.

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. True

  2. False

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Correct Option: B
Explanation:

Relative density is the ratio of density of a substance to the density of a given reference material. Thus, it is a unit less quantity. Hence, the given statement is false.  

Derived units can be defined in terms of one or multiple fundamental units.

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. True

  2. False

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Correct Option: A
Explanation:
The units of fundamental quantities (length, mass,time) are known as fundamental units(meter, kilogram, second).
The derived quantities are the quantities defined in terms of fundamental quantities via a quantitative equation. Hence, the units of these fundamental quantities involved in the equation defines the derived units.
Hence, the given statement is true.

An atmosphere

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. is a unit of pressure

  2. is a unit of force

  3. gives us an idea of composition of air

  4. is the height above which there is no air

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Correct Option: A
Explanation:

An atmosphere is a unit of pressure.

$1$ Pa = $9.87\times 10^{-6}$  atm
Or   $1$ bar $ = 0.987$ atm

Which of the following has derived dimension?

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. Velocity

  2. Acceleration

  3. Density

  4. All of the above 

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Correct Option: D
Explanation:

The fundamental quantities are basically mass, length,  time etc. Velocity is defined as the rate of displacement with respect to time. Displacement has dimensions same as that of length. Velocity is a derived quantity. Acceleration is defined as the rate of change of velocity with respect to time. This is how when acceleration is dependent on time and velocity. It is also a derived quantity. Density is defined as the mass of a unit volume of a substance. Volume has the dimension of the cube of length. Hence density is also a derived quantity.

Which of the following physical quantities has neither dimensions nor unit?

physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

  1. angle

  2. Luminous intensity

  3. Coefficient of friction

  4. Current

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Correct Option: C
Explanation:

Unit of angle is radian, that of luminous intensity is candela and that of current is Ampere. Coefficient of friction is unitless and dimensionless.

Coefficient of friction$=\dfrac{Applied force}{Normal reaction}$
$=\dfrac{[MLT^{-2}]}{[MLT^{-2}]}=$No dimensions
Unit $=\dfrac{N}{N}=$No unit.