Question

In the given figure, balancing of a cardboard on the tip of a pencil is done. The point of support, $G$ is the centre of gravity. Choose the correct option.

• A. $\tau_{M g}$ about $C G=0$
• B. $\tau_{R}$ about $CG =0$
• C. Net $\tau$ due to $m_{1} g, m_{2} g \ldots \ldots m_{n} g$ about $CG =0$
• D. All of the above

Answer 1

Answer: (D)

Point $G$ is the centre of gravity of the cardboard and it is so located that the total torque on it due to forces $m_{1} g , m_{2} g \cdots m_{n} g$ is zero.
It means $\tau_{M g}=\Sigma \tau_{i}=\Sigma r _{i} \times m_{i} g =0$.
$\tau$ of reaction $R$, i.e $\tau_{R}$ about $CG$ is also zero as it is at $CG$.
$\therefore CG$ could be defined as the point, where the total gravitational torque on the body is zero.