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## PowerPoint Slideshow about ' Physics 221 Chapter 11' - jariah

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Physics 221Chapter 11

Problem 2 . . . Angular Momentum

- Guesstimate the formula for the angular momentum?
- A. mv
- B. m
- C. I
- D. 1/2 I

Solution 2 . . . Angular Momentum

- Guesstimate the formula for the angular momentum?
- Linear Momentum is mv
- Angular Momentum is I

Conservation of Angular Momentum

- In the absence of any external torques, the angular momentum is conserved.
- If = 0 then I11 = I2 2

All about Sarah Hughes . . .

Click me!

Problem 3 . . . Sarah Hughes

- A. When her arms stretch out her moment of inertia decreases and her angular velocity increases
- B. When her arms stretch out her moment of inertia increases and her angular velocity decreases
- C. When her arms stretch out her moment of inertia decreases and her angular velocity decreases
- D. When her arms stretch out her moment of inertia increases and her angular velocity increases

Solution 3 . . . Sarah Hughes

- B. When her arms stretch out her moment of inertia increases and her angular velocity decreases
- I11 = I2 2
- So when I increases, decreases!

Vector Cross-Product

- A X B is a vector whose:
- magnitude = |A| |B| sin
- direction = perpendicular to both A and B given by the right-hand rule.
- Right-hand rule: Curl the fingers of the right hand going from A to B. The thumb will point in the direction of A X B

= dL/dt

Proof

L = r x p

dL/dt = d/dt(r x p)

dL/dt = dr/dt x p + r x dp/dt

dL/dt = v x p + r x F

But v x p = 0 because p = mv and so v and p are parallel and sin 00 = 0

dL/dt = r x F

=dL/dt

Solution 4 . . . cross product

= r x F

= (2 i + 3 j) x (- i + 2 j)

= - 2 i x i + 4 i x j - 3 j x i + 6 j x j

= 0 + 4 k + 3 k +0

= 7 k

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