yes but what i'm saying is that the original question was written wrongly as it doesnt travel 3 times faster therefore the question is null and void.
he also asked would the third door move at the speed of light i answered that it didn't; doesn;t mean my answer isn't valid just becuase i applied engineering to it?
OK guys let's puts some figures to this and assume:
the opening is 1800 mm wide
the door is in three sections
the door closes in 10 seconds
OK let's now do the maths;
the leading edge of the first section travels 600 mm in 10 seconds = 0.06 metres/second
the leading edge of the second section travels 1200 mm in 10 seconds = 0.12 metres/second
the leading edge of the third section travels 1800 mm in 10 seconds = 0.18 metres/second
all relative to the lift of course which is stationary
so if I built a door that had 3000 sections in an opening 1800 metres wide
the leading edge of the first section travels 600 mm in 10 seconds = 0.06 metres/second
the leading edge of the second section travels 1200 mm in 10 seconds = 0.12 metres/second
the leading edge of the third section travels 1800 mm in 10 seconds = 0.18 metres/second
.....
the leading edge of the 3000th section travels 1800 metres in 10 seconds = 180.0 metres/second
again relative to the lift of course which is stationary
Now the speed of light = 299 792 458 metres/second so let's put that into round figures 3,000,000 metres/second
so in theory my speed of light door would need to be:
3,000 x 3,000,000/180 = 9,000,000,000/180 = 50,000,000 sections each of 600 mm
operating over an opening width of:
50,000,000 x 0.6 = 30,000,000 metres
E&OE
I hate maths