# A solid disk, spinning counter-clockwise, has a mass of 4 kg and a radius of 7 m. If a point on the edge of the disk is moving at 8 m/s in the direction perpendicular to the disk's radius, what is the disk's angular momentum and velocity?

Oct 30, 2016

The angular momentum is $= 112 k g {m}^{2} / s$
The angular velocity is $= \frac{8}{7} H z$

#### Explanation:

Let's start by calculating the angular velocity
we use the equation
$v = 8 \frac{m}{s}$
$r = 7 m$

$v = r \cdot \omega$
and $\omega = \frac{v}{r} = \frac{8}{7} H z$

The moment of inertia of the solid disc $I = m \cdot {r}^{2} / 2$
So $I = 4 \cdot 7 \cdot \frac{7}{2} = 98 k g {m}^{2}$
Then the angular momentum is $L = I \omega$
so, $L = 98 \cdot \frac{8}{7} = 112 k g {m}^{2} / s$