Special relativity and standard configuration

[greg997]

40s - (0.5c * 20cs) it should have been which gives me 30s/denominator and time t'= 34us
whould that be correct?
so it would take 34us for ship to reach destination -planet B from planet A at 0.5c . That is from ship refrence point?

 

[greg997]

i got numbers wrong..again. i think it should be 34s not us.

 

[greg997]

The "denominator" of which you speak. What is that? Can you show us?

... in my case v =0.5c so the denominator is 866x10^-3.
(40s - (0.5c * 20cs)/c^2)/(866x10^-3)=34 seconds
would that be correct?

 

[jbriggs444]

i got numbers wrong..again. i think it should be 34s not us.

Yes. The ship clocks tick off 34 seconds between $E_1$ and $E_3$.

 

[greg997]

thank you jbriggs444 for confirmation.
How can i calculate velocity of planet B in spaceships reference? and the distance between these two planets from spaceships reference?

 

[jbriggs444]

thank you jbriggs444 for confirmation.
How can i calculate velocity of planet B in spaceships reference? and the distance between these two planets from spaceships reference?

Relative velocities in special relativy are always equal and opposite (assuming that one has aligned the respective coordinate systems with the direction of the relative velocity).

The speed of the rocket in the planet frame is the same as the speed of the planet in the rocket frame.

 

[greg997]

so if the velocity of spaceship is 0.5c from planets refrence then looking from spaceships refrence the planets velocity is -0.5c? makes sense
and distance?

 

[jbriggs444]

so if the velocity of spaceship is 0.5c from planets refrence then looking from spaceships refrence the planets velocity is -0.5c? makes sense
and distance?

Yes, the velocity is -0.5c.

If you multiply that by the [primed] time between $E_1$ (planet A passing) and $E_3$ (planet B passing), that will tell you how far apart the planets must be in the spaceship frame.

 

[greg997]

so in my case , the time was t=34s and velocity v=0.5 , so the distance was 17 cs.

 

[greg997]

that is my first time trying to understand these other refrence frames.
In general, in life we dont really do that.
That special relativity subject is completly diffrent to other areas in physics. It is mind boggling.

thank you all for your help and support. It takes some mental exercise to look at events from diffrent refrence frames , especiayl with speed of light involved.

 

[jbriggs444]

In general, in life we dont really do that.

In real life, we do not often use mathematics to translate measurements from one reference frame to another. But we use reference frames all the time without even stopping to think about it.

We climb into a car (or boat or train) and sit comfortably as the vehicle moves about.

We can fly on an airplane and walk to the bathroom in the back without worrying that we are travelling at 400 miles per hour backward relative to the ground far below.

Many of us have stepped on or off of a moving walkway, leaning into the transition without having to think too much about it. Some of us have played catch on a carousel.

But you are certainly correct that our every day experience with shifting between moving reference frames does not prepare us for the idea that measures of time or of simultaneity can be affected.