Hints for HW 5
General Advice: This is one of the hardest assignments since it involves
resolving a number of complex paradoxes. You need to be creative to be able to
understand and resolve the different paradoxes, but it is worth the effort.
The mathematical skills you need for this
problem set include algebra and how to take a limit (many of you have seen
limits in calculus, but many people don't understand the process; if you
cannot explain it in words to a friend, then you don't really understand it,
and some review, or discussion at office hours is warranted). You
also need to know what a differential is, and how to work with them.
On the physics side, you need to understand what the frequency of light is
and how current flows through a dc circuit to light a light bulb.
Hints on specific problems:
- Problem 6-4: This is problem is not as daunting as it might seem.
You certainly need to know how to take a mathematical limit to understand
what is being said at the first part. Your autobiography of the photon
need not be long-winded, just be sure to include a complete description
of what is happening.
- Problem 6-5: In order to resolve the moving "T", you need
to be sure to know how to determine the time that the front of the "T"
hits the detonator switch, and then determine when the rear of the "T"
can learn that the front has hit... Also, be sure to think in terms of
time-like, space-like, and light-like intervals between specific events.
- Problem 6-7 The issues you have to resolve, if you believe
the light flickers, is why does it flicker in the slider frame (think
about the times of events like when contact is made to the rails, and
when it is broken, and so on). If you believe it does not flicker, then be sure
to discuss how the current flows continuously to the bulb in the rail frame.
If you don't understand how current flows to light a bulb in a dc circuit,
come to office hours to discuss this.
- Problem 6-8 This is a sophisticated problem, requiring a
sophisticated analysis. First, review problem L-14, and its solution, as
similar techniques are needed there. Try to calculate the acceleration
of the front of the rocket and of the rear of the rocket. You should find
there is a
constraint that limits these accelerations. See what the consequence
of that constraint says about the average velocity of the rear of the ship.
Last modified August 11, 2004
Jim Freericks, Professor of Physics,
freericks at physics dot georgetown dot edu