Physics 325, Fall 2006
REVIEW
QUESTIONS #2
and SOLUTIONS
Note:
These are practice problems only.
No credit will be given for their
completion.
Review strategy:
Make sure you know how to set up each of
these problems

grinding out integrals may not be a good use of your time.
Look at the formula sheets carefully
they should contain what you need to
solve the problems.
1) You are driving from Urbana,
Illinois,
to Chicago
in a very fast car, at a speed u
: g(.
You depart Urbana al t
:0
according
to the clock
in your car and a clock
in Champaign.
The car has a length / (front to back) and height h when it is at rest. The distance
to
Chicago
is D, in a frame at rest with respect
to Chicago. Treat Illinois as flat. Don't
worry about gravity.
(.
< D.
a) An observer
standing beside
the road watches
you go past a signpost which is attached
to the ground. How much time elapses
on his clock between
the time when the front of
your car passes
the signpost and when the back of your car passes
the signpost?
b) How much time elapses
on the car's clock between
the time when the front of the car
meets up with the signpost and when the back of the car meets up with the signpost?
c) What is the height of the car, according
to the stationary observer?
d) How much time elapses
on the clock
in Chicago while you are traveling?
e) How much time elapses
on the car's clock while yoii'are traveling?
f) A truck passes
you up at a speed uz:
\zc,
in the reference
frame moving with the car.
How fast is the truck going according
to a groundbased
observer?
g) Draw a spacetime
diagram of your trip in the frame of someone
at rest with respect
the ground. Indicate the paths in spacetime of Champaign, Chicago, your car, and the
truck. Draw a spacetime diagram
in the frame moving with the truck, showing
the same
spacetimes
paths.
2) For photons, E
: pc. A photon of .n.rgy E is traveling
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 Fall '09
 Lamb
 Physics, mechanics, Trigraph, nd, uch t ime, ignposta nd

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