Quiz #6

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Multiple choice: 1 pt. each

1. A rocket ship zooms by at half the speed of light, and you notice that it is Lorentz contracted. Meanwhile, someone on the ship notices that you're

A. Lorentz expanded.

* B. Lorentz contracted.

C. neither contracted nor expanded.

D. either contracted or expanded depending on the direction the rocket's traveling.

2. Someone on a moving train is pointing a flashlight in the direction of the train's motion. You're on stationary ground and you notice that the speed of light is m/s. The guy on the train measures the light to be traveling at a speed

* A. equal to c.

B. less than c.

C. greater than c.

D. unknown. We need to know the train's speed.

3. An astronaut blasts off into space and goes on a voyage at 90% the speed of light. When he returns to earth and visits his twin brother, he notices that

A. he's still the same age as his twin.

B. he's older than his twin.

* C. he's younger than his twin.

D. each twin sees the other as being younger.

4. Two spaceships are traveling toward each other, each with a speed . The relative speed of one ship measured by the other is

A. zero.

B. c/4

C. c/2

* D. none of the above.

5. Which of the following is a consequence of the fact that nothing in the universe can travel faster than the speed of light c?

A. The kinetic energy of an object has no upper bound.

B. The momentum of an object has no upper bound.

C. The distance a human can travel before dying has no upper bound (assuming a ship exists than can travel arbitrarily fast).

* D. all of the above.

6. The students of PHYS 231-232 love the class because

A. it has given them greater insight into the way things in this world work.

B. it has challenged them to think critically.

C. the TA is way cool.

* D. all of the above.

7. A supertrain (rest length = 100 m) travels at a speed of .95c as it passes through a tunnel (rest length = 50 m). As seen by a trackside observer, is the train ever completely within the tunnel? If so, by how much?

The train fits inside the tunnel by 50-31.22=18.8m.