Question: The mechanical quantity, which has dimensions of reciprocal of mass $\left(\mathrm{M}^{-1}\right)$ is :
A) angular momentum
B) coefficient of thermal conductivity
C) torque
D) gravitational constant
Answer: gravitational constant
Solution:
$$ \begin{aligned} & \text { Angular momentum }=\left[\mathrm{ML}^2 \mathrm{~T}^{-1}\right] \ & \text { Coeff of thermal conductivity }=\left[\mathrm{MLT}^{-3} \mathrm{~K}^{-1}\right] \ & \text { Torque }=\left[\mathrm{ML}^2 \mathrm{~T}^{-2}\right] \ & \text { Gravitational constant }=\left[\mathrm{M}^{-1} \mathrm{~L}^3 \mathrm{~T}^{-2}\right] \end{aligned} $$
So, gravitational constant has power of $(-1)$ of $\mathrm{M}$.
