# A cylinder has inner and outer radii of 4 cm and 18 cm, respectively, and a mass of 1 kg. If the cylinder's frequency of counterclockwise rotation about its center changes from 15 Hz to 16 Hz, by how much does its angular momentum change?

Nov 14, 2017

The change in angular momentum is $= 0.11 k g {m}^{2} {s}^{-} 1$

#### Explanation:

The angular momentum is $L = I \omega$

where $I$ is the moment of inertia

and $\omega$ is the angular velocity

The mass of the cylinder is $m = 1 k g$

The radii of the cylinder are ${r}_{1} = 0.04 m$ and ${r}_{2} = 0.18 m$

For the cylinder, the moment of inertia is $I = m \frac{\left({r}_{1}^{2} + {r}_{2}^{2}\right)}{2}$

So, $I = 1 \cdot \frac{\left({0.04}^{2} + {0.18}^{2}\right)}{2} = 0.017 k g {m}^{2}$

The change in angular velocity is

$\Delta \omega = \Delta f \cdot 2 \pi = \left(16 - 15\right) \times 2 \pi = 2 \pi r a {\mathrm{ds}}^{-} 1$

The change in angular momentum is

$\Delta L = I \Delta \omega = 0.017 \times 2 \pi = 0.11 k g {m}^{2} {s}^{-} 1$