Question

Unit of work in MKS system is
A. Calorie
B. Newton
C. Joule
D. Watt

Answer 1

Hint: A complete set of units which is used to measure all kinds of fundamental and derived quantities is called a system of units. The physical units which can neither be derived front one another, nor they can be further resolved into more simpler units are called fundamental units. All the other physical units which can be expressed in terms of the fundamental units are called ts derived units

Complete answer:
Although the number of physical quantities we measure is very large, we don’t need a very large number of units because various physical quantities are interrelated and can be expressed as in terms of just seven fundamental units.
The physical units which can neither be derived front one another, nor they can be further resolved into more simpler units are called fundamental units. The units of fundamental quantities such as mass, length, etc. are fundamental units.
Derived units are those units which can be expressed in terms of fundamental units. e.g. unit of speed
\[\text{Speed=}\dfrac{\text{distance travelled}}{\text{time taken}}\],
$\therefore \text{ Unit of speed=}\dfrac{\text{Unit of distance}}{\text{Unit of time}}=\dfrac{\text{meter}}{\text{second}}=m{{s}^{-1}}$
System of units: A complete set of units which is used to measure all kinds of fundamental and derived quantities is called a system of units. Some commonly used system of units are
(i)CGS system: It was set up in France. it is based on centimetre, gram and second as the fundamental units of length, mass and time respectively.
(ii) FPS system: It is a British system based on foot, pound and second as the fundamental units of length, mass and time respectively.
(iii)MKS system: It is also a French system based on metre, kilogram and second as the fundamental units of length, mass and time respectively.
(iv)SI: The international system of units. It covers all branches of science and technology. It is based on seven basic units and two supplementary units.
 In SI system the seven basic units are meter(m), kilogram(kg) ,second(s), kelvin(K), ampere(A), candela(cd) and mole(mol) are used for seven basic fundamental quantity as Length, Mass, Time, Temperature, Electric current, Luminosity intensity and Quantity of matter respectively.
Workdone is a measure of energy transfer when a force(F) moves an object by a distance (d).
So $\text{Workdone=Force}\times \text{Displacement}$, so
\[\text{Unit of work done in MKS=Unit of force in MKS unit}\times \text{Unit of displacement in MKS unit}\]
Unit of Force in MKS unit is Newton(N) and unit of displacement in MKS unit is Meter(m)
So the unit of work done will be $\text{Newton }\!\!\times\!\!\text{ Meter}$. Which is known as Joule.
So one joule is the amount of work when one Newton force displaces a body by one meter.
So the unit of Work in the MKS unit is joule.
So the correct option is. C. Joule

Note:
The CGS,MKS and SI are metric or decimal systems of units. This is because the multiples and submultiples of their basic units are related to the practical units by powers of 10. The fps system is not a metric system. This system is not in much use these days.
In CGS units the unit of work is erg.$1erg={{10}^{-7}}Joule$.