Relativity (Length Contraction)

Question

A 1-meter long spear is thrown at a relativistic speed through a pipe that is 1 meter long. Both of these dimensions are measured when each is at rest. When the spear passes through the pipe, which of these statements best describes what is observed?

a .The spear shrinks so that the pipe completely covers it at some point.

b. The pipe shrinks so that the spear extends from both ends at some point.

c. Both shrink equally so the pipe completely covers it at some point.

d. Any of these, depending on the motion of the observer.

Answer 1

d.

Here's a good video describing what happens.

http://www.youtube.com/watch?v=nNgzqpKZw...

Answer 2

It depends on the observer. Say you are the observer.

If you are located outside the pipe and you are at rest, the obvious answer is letter a because of length contraction according to einstein.

If you are moving with the same speed as the moving spear, then c is the answer.

But when the spear is the frame of reference and you assume the spear is the one at rest and the pipe is moving towards you, the answer is letter b.

In short, the correct answer is letter d.

Answer 3

everyone seems to be adding baggage to your question. given the parameters you stated the correct ans is a.

Answer 4

d.  If you're moving at relativistic speed relative to me, two events which one of us judges to be simultaneous won't appear simultaneous to the other.So there's no paradox.  This is made clearer by the following story.  A spaceship 10 m long whizzes at relativistic speed through a paint sprayer 10m long, the sprayer turns on all the spray nozzles simultaneously and the spaceship later slows down and the pilot meets the paint sprayer.  Obviously they've both got to agree whether or not the spaceship was sprayed all over.  The sprayer says, well, your spaceship was contracted and I sprayed it when it was inside the spray booth so it's painted all over.  The pilot says sure it's painted all over, even though your spray booth was shorter than the spaceship, but that's because you turned on the nozzles at different times.