Q161 / 180 · COMEDK 2014 · Physics
Which two of the following quantities are dimensionally equivalent?
- A(i) and (ii)
- B(i) and (iii)
- Correct answerC(ii) and (iii)
- D(ii) and (iv)
Solution
We know that,
Force $=$ Mass $\times$ Acceleration
$\Rightarrow \quad F=m \times a$
$\Rightarrow \quad[F]=[\mathrm{m}][\mathrm{a}]=[\mathrm{M}]\left[\mathrm{LT}^{-2}\right]=\left[\mathrm{MLT}^{-2}\right]$
Pressure $(p)=\frac{\text { Force }(F)}{\operatorname{Area}(A)}$
$\Rightarrow \quad[p]=\frac{[\mathrm{F}]}{[\mathrm{A}]}=\frac{\left[\mathrm{MLT}^{-2}\right]}{\left[\mathrm{L}^{2}\right]}=\left[\mathrm{ML}^{-1} \mathrm{~T}^{-2}\right]$
Young's modulus, $Y=\frac{\text { Stress }}{\text { Strain }}$
$\Rightarrow \quad[Y]=\frac{[\text { Stress }]}{[\text { Strain }]}=\frac{[F / A]}{[\text { Strain }]}$
$=\frac{\left[\mathrm{ML}^{-1} \mathrm{~T}^{-2}\right]}{\left[\mathrm{M}^{0} \mathrm{~L}^{0} \mathrm{~T}^{0}\right]}$
$=\left[\mathrm{ML}^{-1} \mathrm{~T}^{-2}\right]$
Energy $=$ Work done $=$ Force $\times$ Displacement
$\Rightarrow[$ Energy $]=[$ Force $] \times[$ Displacement $]$
$=\left[\mathrm{MLT}^{-2}\right][\mathrm{L}]=\left[\mathrm{ML}^{2} \mathrm{~T}^{-2}\right]$
Hence, we see that dimensions of pressure and Young's modulus is same.
Hence, the correct answer is option: 'C'.