Tag: units - definitions and systems

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Questions Related to units - definitions and systems

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Which of the following pairs of physical quantities have same dimensions?

  1. Force and power

  2. Torque and energy

  3. Torque and power

  4. Force and torque
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Torque is the moment of force given by:$ \vec\tau=\vec r\times \vec F$

It’s unit is Newton-meter.

The unit of work/energy is also Newton-meter or Joule.

Thus, both of these physical quantities have the same units/dimensions.

$[Torque]=[M][L]^{2}[T]^{−2}=[Energy]$
Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Which of the following statements is incorrect regarding mass. ?

  1. It is a basic property of matter.

  2. The SI unit of mass is kg.

  3. The mass of an atom is expressed in u.

  4. It depends upon the temperature, pressure or location of the object in space.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Mass is property of mater, which is independent of other properties like temperature, pressure or location of the object in space.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Which of the following is unitless quantity?

  1. Pressure gradient

  2. Displacement gradient

  3. Force gradient

  4. Velocity gradient
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The gradient of any physical quantity is computed to as per unit length. This means it is a rate with respect to length. So, the Displacement gradient will also be length per unit length. Because a displacement gradient is the ratio of two quantities having dimensions of "length". That is, a displacement gradient has units of a meter per meter for example. 

The length dimensions will be cancelled, and we have a unitless quantity. While others will be having certain units. Hence it is a unitless quantity.

Thus option B is correct.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

An atmosphere:

  1. Is a unit of pressure

  2. Is a unit of force

  3. Gives an idea of the composition of air

  4. Is the height above which there is no atmosphere
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An atmosphere is defined as the unit of pressure because we use to write the atmospheric pressure in terms of the $atm$.


So, it is a unit of pressure. Option $A$ is correct.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

In a screw gauge, 5 complete motations of the screw cause it to a linear distance of 0.25 cm. There are 100 circular scale divisions. The thickness of a wire measured by this screw gauge gives a reading of 4 main scale divisiors and 30 circular scale divisions. Assuming negligible zero, the thickness of the wire is:

  1. $0.4300$ cm
  2. $0.2150$ cm
  3. $0.3150$ cm
  4. $0.0430$ cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
In one rotation, scale moves $\dfrac{0.25}{5}=0.05\,cm$

Least count $=0.05\times 10^{-2}\,cm$

For $4$main scale division $=4\times 0.05=0.2\,cm$

For circular scale division $30\times 0.05\times 10^{-2}=1.5\times 10^{-2}\,cm$

Thickness of wire $0.2+0.015=0.2150\,cm$
Multiple choice physics dynamics - explaining motion physical quantities motion and measurement units - definitions and systems

In particular system of unit, if the unit of mass becomes twice and that of time becomes half, then $8$ Joules will be written as _______ units of work

  1. $16$
  2. $1$
  3. $4$
  4. $64$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The unit of work is $kg\ m^2/s^2$.

$8Joule=\dfrac { 8M{ L }^{ 2 } }{ { T }^{ 2 } }$

$ =\dfrac { 8(1kg){ (1m) }^{ 2 } }{ { (1s) }^{ 2 } } $

On doubling the unit of mass and unit of time is halved:
$=\cfrac { 8(2\quad unit\quad of\quad mass){ (1m) }^{ 2 } }{ { \left( \frac { 1 }{ 2 } unit\quad of\quad time \right)  }^{ 2 } }$

$ =\dfrac { 8\times 2 }{ { \left( \frac { 1 }{ 2 }  \right)  }^{ 2 } } units\quad of\quad work\\ =64\ units\quad of\quad work.$