# Homework Help: QUeston on lorentz transformation

1. Apr 8, 2007

### TKDyl

Hey, im new... A good friend of mine told me that i could come here if i ever needed help in physics... Well now is really a bad time to tell you guys this... but i have a final exam in 2 days...

Im having a problem to solve this question maybe you could guide me some how

Quote " A starship voyages to a distant planet 10 lyr away. The explores stay 1 yr, return at the same speed, and arrive back on earth 26 years after they left. Assumer that the time to accelerate and decelerate are negligible.
A)what is the speed of the starship.

The problem i think i'm setting the problem right, its just i get a quadratic equation when i do. and im not sure if this is right.

If anyone could guide me it would be greatly appreciated

2. Apr 8, 2007

### Staff: Mentor

Please show the work that you've done so far, and the quadratic equation that you got as a result. Then it will be much easier for people to help you by pointing out what you did wrong. Otherwise we have to guess blindly, or simply give you the solution (which is against the rules of this forum).

3. Apr 9, 2007

### Ballon

well, look at this, if the speed was the speed of the light C , it would have been 10 years to go , 1 years to explaore and 10 years to come back, so total 21 years, obviously it is not the answer, but what can you learn from this ?

4. Apr 9, 2007

### TKDyl

lol of course if it would be that easy :P, but no, i know what the answer is, its in back of the book, i just don't know how to get it. For the quadratic formula... your going to have to wait till tonight... I threw away the paper with all my work cause i believed it to be wrong. I can re do it... im just studying for chem because that is my first exam.

5. Apr 9, 2007

### Boustrophedon

Assuming you mean 26 years experienced by the explorers means a journey of 20 lightyears in 25 years or 4 lightyears in 5 years. So 4/v is the "stationary" time which is also equal to gamma times travel time = 5.gamma. Thus 4.sqrt(1-v.v) = 5v and hence 41 v squared equals 16 which gives a v = 0.624695c or almost 5/8 the speed of light, which is the correct answer no doubt ?

Last edited: Apr 10, 2007