Question

Two discs have same mass and thickness. Their materials have densities $d_1$ and $d_2$, then their MOl about central axis will be

• A. $d_1 : d_2$
• B. $d_1 d_2: 1$
• C. $1:d_1 d_2$
• D. $d_2: d_1$

Answer 1

Answer: (D)

$d_2: d_1$

Answer 2

Here $m_1 = m_2 = m$ so $\pi r^2_1 d_1 = \pi r^2_2 d_2$ $i.e. \frac{r^2_1}{r^2_2} = \frac{d_2}{d_1}$ $\frac{I_1}{I_2} = \frac{\frac{1}{2} mr^2_1}{\frac{1}{2} mr^2_2} = \frac{r^2_1}{r^2_1} = \frac{d_2}{d_1}$