• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Spaceship Special relativity

  • Thread starter struggles
  • Start date
50
0
1. Homework Statement
  1. A spaceship travels from Earth to the vicinity of the star that is measured by astronomers on Earth to be six light-years away. The spaceship and its occupants have a total rest mass of 32 000 kg. Assume that the spaceship travels at constant velocity. The time taken as measured by clocks on the spaceship is 2.5 years.
    1. (i) Compute the velocity of the spaceship. [3 marks]

    2. (ii) How long does the trip take as measured by clocks in the Earth’s

      inertial rest frame? [3 marks]

2. Homework Equations

x' = γ(x-ut)
t' = γ(t - ux/c2) where the dash frame is the object rest frame, u is the relative speed between frames
γ = 1/√(1-u2/c2)
v' = v-u/1-u2v/c2
3. The Attempt at a Solution

So I'm a bit stuck my the first part of the question.
So far I have determined that x = 6ly, t' = 2.5yrs. I'm getting a bit puzzled as to what I'm looking to find. Is it u
or v or are they the same thing in this case? regardless I cannot think of a way in which i have enough variables that allows me to compute a value. Any help would be greatly appreciated!
 

Doc Al

Mentor
44,803
1,061
Sometimes you have to chip away at it. See if you can solve for x'. (Hint: You'll need a different version of your first equation.)

I'm getting a bit puzzled as to what I'm looking to find. Is it u
or v or are they the same thing in this case?
You are solving for u. v is irrelevant: there's only one velocity in this problem.
 
50
0
Ok so I'm not sure if this works or not but this is what I've got:
t = γt' and t = x/u.
Combining this gives x/t' = uγ and then expanding this all out and rearranging gives a value for u. Would this method work?
 

Doc Al

Mentor
44,803
1,061
Ok so I'm not sure if this works or not but this is what I've got:
t = γt' and t = x/u.
Combining this gives x/t' = uγ and then expanding this all out and rearranging gives a value for u. Would this method work?
That will do it. Good! :thumbup:
 
50
0
Thank you for your help!
 

Want to reply to this thread?

"Spaceship Special relativity" You must log in or register to reply here.

Related Threads for: Spaceship Special relativity

  • Posted
Replies
0
Views
850
  • Posted
Replies
1
Views
865
  • Posted
Replies
5
Views
1K
Replies
3
Views
1K
Replies
1
Views
540
Replies
9
Views
492
Replies
0
Views
1K
Replies
1
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top