# Physics 1304/1404 - Spring 1999

# Homework Assignment #9 - Optional

**Due:** Wednesday 5 May 1999 (at the start of the final exam)

### READING

Chapter 39.
### QUESTIONS

Chapter 39 - 3, 4, 10, 11.
### PROBLEMS

Chapter 39 - 5, 6, 9, 14, 18, 37.
### ANSWERS

These are the ANSWERS only, not the SOLUTIONS. It is not sufficient to
copy these and turn them in as homework. You must show your work.
**Q 39-3)** The observer on Earth would see the astronaut shrunk in the
direction in which the astronaut is traveling. The other two perpendicular
directions would be unaffected. For example, if the astronaut is facing
the front of the ship, the observer on Earth would see the astronaut as
thinner from front to back, but just as wide from side to side and just
as tall as at rest.

The observer on Earth would measure the astronaut's pulse to be slower
than normal.

The astronaut would not measure these changes in himself, but the astronaut
measures the Earth-bound observer to be shrunk in one dimension, and to
have a slower pulse. (Each sees the other as slowed down!)

**Q 39-4)** The clock which is moving eastward runs slower. When the
clocks are brought back together, they are no longer synchronized; the
Earth-bound clock has moved ahead.

**Q 39-10)** The mass of an object increases by the gamma factor. The
volume of an object shrinks by the gamma factor; one dimension (say length)
shrinks while the other two (width and height) do not change. The
relativistic density m/V therefore increases by (gamma)^{2}.

**Q 39-11)** The speed of light is always c = 3 x 10^{8} m/s,
no matter what the source is doing (receding or approaching).

**P 39-5)**
- 60 m/s
- 20 m/s
- 44.7 m/s

**P 39-6)** 0.886 c

**P 39-9)** 0.8 c

**P 39-14)**
- 1.37 y
- 1.31 lightyears

**P 39-18)** 0.357 c

**P 39-37)** 4.2 billion kilograms per second!

Please report any corrections to
Professor Scalise.

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