7.5. It's a rough approximation, but let's treat a spinning ice skater as a solid cylinder with a radius of 0.25 m. (a) If their mass is 55 kg, what is their rotational inertia? (b) Calculate the magnitude of the angular momentum of a 55 kg ice skater spinning 6 times a second. (c) Calculate the total kinetic energy of this skater if they are spinning at a rate of 6 rotations per second while traveling through the air at a rate of 2 m/s.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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I need help on question 7.5?

## 7.4 Vector Cross Product

**Given:**
\[
\vec{A} = 
\begin{bmatrix} 
4.0 \, \text{m} \\ 
-2.0 \, \text{m} 
\end{bmatrix}
\quad \text{and} \quad
\vec{B} = 
\begin{bmatrix} 
-2.0 \, \text{N} \\ 
5.0 \, \text{N}
\end{bmatrix}
\]

**(a)** Draw a diagram with both vectors starting at the origin and express both vectors as magnitude and direction. What is the angle between the two vectors?

**(b)** Show that \(\vec{A} \times \vec{B} = 16 \, \text{Nm} \, \hat{z}\) by using the formula \(|\vec{A}||\vec{B}|\sin\theta\) and the right-hand rule.

**(c)** Find \(\vec{A} \times \vec{B}\) by using matrix multiplication: \((A_xB_y - A_yB_x)\hat{z}\).

---

## 7.5 Rotational Dynamics of an Ice Skater

It’s a rough approximation, but let’s treat a spinning ice skater as a solid cylinder with a radius of 0.25 m.

**(a)** If their mass is 55 kg, what is their rotational inertia?

**(b)** Calculate the magnitude of the angular momentum of a 55 kg ice skater spinning 6 times a second.

**(c)** Calculate the total kinetic energy of this skater if they are spinning at a rate of 6 rotations per second while traveling through the air at a rate of 2 m/s.
Transcribed Image Text:## 7.4 Vector Cross Product **Given:** \[ \vec{A} = \begin{bmatrix} 4.0 \, \text{m} \\ -2.0 \, \text{m} \end{bmatrix} \quad \text{and} \quad \vec{B} = \begin{bmatrix} -2.0 \, \text{N} \\ 5.0 \, \text{N} \end{bmatrix} \] **(a)** Draw a diagram with both vectors starting at the origin and express both vectors as magnitude and direction. What is the angle between the two vectors? **(b)** Show that \(\vec{A} \times \vec{B} = 16 \, \text{Nm} \, \hat{z}\) by using the formula \(|\vec{A}||\vec{B}|\sin\theta\) and the right-hand rule. **(c)** Find \(\vec{A} \times \vec{B}\) by using matrix multiplication: \((A_xB_y - A_yB_x)\hat{z}\). --- ## 7.5 Rotational Dynamics of an Ice Skater It’s a rough approximation, but let’s treat a spinning ice skater as a solid cylinder with a radius of 0.25 m. **(a)** If their mass is 55 kg, what is their rotational inertia? **(b)** Calculate the magnitude of the angular momentum of a 55 kg ice skater spinning 6 times a second. **(c)** Calculate the total kinetic energy of this skater if they are spinning at a rate of 6 rotations per second while traveling through the air at a rate of 2 m/s.
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