## In the twin paradox example done in lecture, just before Alice arrives at the star (before she slows down), she observes Bob’s clock back where he is located. (In other words, she has a photo taken of his clock and her corresponding clock at that location, her clock being part of her lattice of clocks.) Compared to her clock, does she observe Bob’s clock to be behind, ahead, or the same time as hers?

9. Question 9 In the twin paradox example done in lecture, just before Alice arrives at the star (before she slows down), she observes Bob’s clock back where he is…

## Which world line represents an object moving to the right along the x axis and slowing down (decelerating)?

10. Question 10 Which world line represents an object moving to the right along the x axis and slowing down (decelerating)? 1 point

## Consider Bob on Space Station Omega. At time t = 0, Alice flies by in her spaceship at constant velocity, heading to the right. She then quickly reverses direction and heads back to the left, but stops and remains motionless (compared to Bob) before she reaches Bob’s position. Which diagram represents Alice’s world line in Bob’s frame of reference?

8. Question 8 Consider Bob on Space Station Omega. At time t = 0, Alice flies by in her spaceship at constant velocity, heading to the right. She then quickly…

## One way to synchronize a system of identical (and well-running) clocks is to use one master clock to set the other clocks, and then move the clocks to their various locations. What is a potential problem with this approach that was mentioned in the lecture?

1. Question 1 One way to synchronize a system of identical (and well-running) clocks is to use one master clock to set the other clocks, and then move the clocks…

## Consider a train with three cars, moving to the right past Alice, who is on a train station platform. The front of the first car reaches Alice at time t = 0. In Alice’s frame of reference, which set of world lines represents the world lines of the three cars? (Let a world line represent the front of the car.)

7. Question 7 Consider a train with three cars, moving to the right past Alice, who is on a train station platform. The front of the first car reaches Alice…

## Consider Bob on Space Station Omega in deep space. At time t = 0, both Alice and Kris fly by Bob heading to the right at the same velocity, with Alice in the lead. (Alice passes by Bob at t = 0, with Kris slightly behind her.) Which diagram represents the world lines of Alice and Kris in Bob’s frame of reference?

6. Question 6 Consider Bob on Space Station Omega in deep space. At time t = 0, both Alice and Kris fly by Bob heading to the right at the…

## 3. Question 3 Consider person #1 moving to the right (positive x direction) at a constant velocity v with respect to person #2. Assume that at time t = 0 the two were side by side. Each person measures distances using the same units (such as meters), and each person uses their own location as the origin for their measuring system. Let the measurements of person #1 be represented by x1 and the measurements of person #2 be represented by x2. Consider an event that happens at some position x2 and time t (after time t = 0), according to person #2. Person #1 measures the location of this event at position x1. Would the value of x1 be greater than or less than x2? 1 point x1 will be greater than x2 x1 will be less than x2

3. Question 3 Consider person #1 moving to the right (positive x direction) at a constant velocity v with respect to person #2. Assume that at time t = 0…

## Consider person #1 moving to the right (positive x direction) at a constant velocity v with respect to person #2. Assume that at time t = 0 the two were side by side. Each person measures distances using the same units (such as meters), and each person uses their own location as the origin for their measuring system. Let the measurements of person #1 be represented by x1 and the measurements of person #2 be represented by x2. Consider an event that happens at some position x2 and time t (after time t = 0), according to person #2. Person #1 measures the location of this event at position x1. Would the value of x1 be greater than or less than x2?

3. Question 3 Consider person #1 moving to the right (positive x direction) at a constant velocity v with respect to person #2. Assume that at time t = 0…

## Alice creates a machine that can shoot basketballs in a horizontal direction. Using a radar gun, Bob measures the speed of the basketball coming from the machine when it is stationary and finds that it is 30 km/hour. If Alice then puts the machine on top of a car, which she is driving at 50 km/hour toward Bob, and shoots a basketball in the direction of travel, what would be the horizontal speed of the ball as Bob measures it? (Neglect any effects of air resistance or other sources of friction.)

12. Question 12 Alice creates a machine that can shoot basketballs in a horizontal direction. Using a radar gun, Bob measures the speed of the basketball coming from the machine…

## True or false: The special theory of relativity applies only to inertial frames of reference.

11. Question 11 True or false: The special theory of relativity applies only to inertial frames of reference. 1 point   True False