Question

Which of the following is not a unit of displacement?
(A) \[{\text{m}}\]
(B) \[{\text{cm}}\]
(C) \[{\text{km}}\]
(D) \[{\text{m}} \cdot {{\text{s}}^{{\text{ - 1}}}}\]

Answer 1

Hint: Recall the definition of displacement. Check which of the fundamental physical quantities is explained by the definition of the displacement. Recall the various units of that fundamental physical quantity and compare those units with the units in the options given.

Complete step by step answer:
The displacement of an object is the distance between the initial and final position of the object. Hence, the displacement of an object is the length of path between the initial and final position of the object.There are some units of length such as meter, centimeter and kilometer which are denoted by the symbols\[{\text{m}}\], \[{\text{cm}}\] and \[{\text{km}}\].Hence, meter, centimeter and kilometer are the units of displacement.The unit \[{\text{m}} \cdot {{\text{s}}^{{\text{ - 1}}}}\] involves the unit of length as well as time. From this unit, one can determine that this is the unit of a physical quantity which involves the division of length and time. There is only one physical quantity that involves the division of length and time which is velocity. Therefore, \[{\text{m}} \cdot {{\text{s}}^{{\text{ - 1}}}}\] is the unit of velocity and not displacement.So, \[{\text{m}} \cdot {{\text{s}}^{{\text{ - 1}}}}\] is not the unit of displacement.

Hence, the correct option is D.

Note:The students may get confused that meter is the SI unit of the length, so that the unit of displacement from the given options is meter only denoted by symbol m. But centimeter (cm) and kilometer (km) are also the units of length and they can be converted into the SI unit of length that is meter by using appropriate conversion factor.