Two spacecraft going in opposite directions at 3/4 of the speed of light.?

Question

One spacecraft has an endless spool of thread attached to the back end with the free end of the thread attached to the spacecraft going in the opposite direction. What is the linear velocity at the edge of the spool? Say the spool is 2ft. in diameter.

Answer 1

It should be the same linear velocity as the thread. So 2 times the 3/4.

Answer 2

I think most people did not get the question right. The velocity in question is of the spool not the thread or the rockets. With simple physics it seems to be having a linear velocity of 1.5c on the edge. But that won't happen. Let's consider a simpler experiment.. something is moving at only 0.01c and by using gears you create a ratio of 1000. So will that cause the other end of gear train to go at a speed of 10c; ofcourse not, because that's not possible. Instead when the velocity of at the end of gear train nears c, it will cause the source of motion to slow down. So no particle in the whole system will ever reach a velocity of c.

Answer 3

There is a relativistic formula for the summation of velocities, which is the situation here. A linear addition of the velocities gives 1.5c, which is impossible. Unfortunately, I can't remember the formula, but I do have it in one of my many books on relativity. If I find it I will edit this answer, unless someone else knows it and answers here. All I can say is that it will be less than c but more than 3/4 c

Edit:

The formula is,

vr = (v1 +v2)/(1 + v1*v2/c^2)

For v1 = v2 = .75c, the relative veloctity is 0.96c

Answer 4

Because of relativity, there simply is no answer. one could say the string has no velocity, and the two rockets are each moving away from the string at 3/4 light speed.Or one could say that the string is moving at .75 light speed, toward a rocket moving at a relative speed of .75 light speed, leaving the remaing rocket traveling with a velocity of zero. Each answer, and every variation of the answer is equally correct, and so a true speed cannot be dtermined.

Answer 5

when you're gazing, you word both beams coming near the assembly element on the speed of light (in although medium that is), so the ultimate speed of both beams is two times the speed of light, so a techniques as you difficulty. even if Einstein reported that not some thing can commute speedier than mild, that doesn't ward off 2 issues ultimate at a larger speed in the eyes of a detached observer, as no "element" is actual travelling speedier than mild. although, even as it is composed of understanding how each and every mild beam thoughts the "collision", for sure relativity should be taken under consideration. in case you've been driving at (really a lot) the speed of light at evening, then mild from the headlamps of a motor vehicle coming any incorrect way may, so a techniques as you difficulty, attain your eyes at precisely the speed of light, not at (really a lot) two times the speed of light.

Answer 6

I'm assuming this question is equivalent to "What's the speed of the rockets in relation to each other?"
Newtonian physics says that it would be 1.5 x c, but since we're dealing with relativistic speeds, and nothing can go faster than c it would in fact be pretty much c.

Answer 7

Responder gp4rts is correct.

Answer 8

279423 miles/second

Answer 9

(U − mU) /σU mU = n1n2 / 2.
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p(Y > X) + 0.5p(Y x X)

Clear?