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# Which of the following is NOT a measure of energy?A) \[Js\] B) \$Ws\$ C) \$kWh\$ D) \$Erg\$

Last updated date: 09th Sep 2024
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Hint: It is a problem in which we check correctness of units for a physical quantity. Use the formula and definition of energy for comparing the left hand side and right hand side of the relation. In case of correct units, both the sides will produce the same results.

Formula used:
\$E = F.s\$
Where, \$E\$ is energy of an object, \$F\$ is applied force on the object, \$s\$ is total displacement of the object.

The S.I. unit for energy is \$Joule(J)\$, for force it is \$Newton(N)\$ or \$kgm{s^{ - 2}}\$ and for displacement it is \$m\$.
Now if we put the formula in terms of units of respective items, we get \$J = kg{m^2}{s^{ - 2}}\$ .
Similarly, the c.g.s unit of energy is \$erg(gc{m^2}{s^{ - 2}})\$
Let’s start analysing the options.

For option A, we get
\$Js = kg{m^2}{s^{ - 1}}\$

For option B, we get
\$Ws = kg{m^2}{s^{ - 2}}\$, because if we expand \$W\$ (watts) like we have done energy, we will get its S.I. unit to be \$kg{m^2}{s^{ - 3}}\$.

For option C, we get
\$kWh = kg{m^2}{s^{ - 2}}\$ in the same way as option B.

For option D,
\$erg\$ is the c.g.s unit for energy.

So the correct answer is option A, because it does not correspond with units (S.I. or c.g.s. system).