Consider the world line of an object drawn on a Minkowski (space-time) diagram. At any point in that space, the slope of that line is: 1. larger than 1 2. less than 1 3. able to take on any value Note: * Correct answer: A

## Annoucements * Last Quiz (This Friday) * Use special relativity to determine the time between signals * Discuss if events are timelike or spacelike separated and how you know * Explain why two events could occur at the same place (or time) * Last Homework * Due next Friday NOT Monday! No project problem * Rest of class * Finish up Relativity (next Monday-ish) and discuss E&M in general (next Wednesday-ish) * Extra credit assessment (next Friday)

Points that lie outside the light cone for a given event are: 1. accessible no matter where they are 2. accessible for given world lines (trajectories) 3. always inaccessible Note: * Correct answer: C

The space time interval is defined by: $$I\equiv x^2 + c^2t^2$$ Events with common space time intervals lie on a hyperbole of constant $I$. **True or False:** A Lorentz boost can allow you to shift between different hyperboles. 1. True 2. False Note: * Correct answer: B

Consider the product of the speed of light and the proper time: $c\,d\tau$. Is this quantity invariant? 1. Yes 2. No 3. I don't know how to tell Note: * Correct Answer: A

Is this "4-velocity" a contravariant 4-vector? $$\eta^{\mu} \equiv \dfrac{dx^{\mu}}{d\tau}$$ 1. Yes 2. No 3. I don't know how to tell Note: * Correct Answer: A

What is $\dfrac{dt}{d\tau}$? 1. $\gamma$ 2. $1/\gamma$ 3. $\gamma^2$ 4. $1/\gamma^2$ 5. Something else Note: * Correct Answer: A

With $\eta^0 = c\gamma$ and $\vec{\eta}=\gamma\vec{u}$, what is the square of $\eta$? $$\eta^2 \equiv \eta \cdot \eta = \eta_{\mu}\eta^{\mu}$$ 1. c^2 2. u^2 3. -c^2 4. -u^2 5. Something else Note: * Correct Answer: C

The momentum vector $\vec{p}$ is given by, $$\vec{p} = \dfrac{m\vec{u}}{\sqrt{1-u^2/c^2}}$$ What is $|\vec{p}|$ as $u$ approaches zero? 1. zero 2. $m\,u$ 3. $m\,c$ 4. Something else Note: * Correct Answer: B