# Homework Help: Traveling spaceships - relativity

1. Sep 6, 2007

### tacosareveryyum

1. The problem statement, all variables and given/known data
2 spaceships traveling in opposite directions pass one another at a relative speed of 1.25x18^8 m/s. The clock on one spaceship records a time duration of 9.1x10^-8 seconds for it to pass from the front end to the tail end of the other ship. What is the length of the second ship as measured from its own rest frame?

2. Relevant equations
lorentz transformations

3. The attempt at a solution
Okay so I am guessing that the second ship, as measured from its rest frame should be smaller that measured from the frame of the other ship.
I used the basic equation v=x/t and plugged in my relative speed of 1.25x10^8 m/s and my time 9.1x10^-8 s. I got 11.38 m as the length measured by the first ship. Then I used the lorentz transformation for length and found the length of the second ship to be 10.34 m.

2. Sep 6, 2007

### Gokul43201

Staff Emeritus
Should it? Who measures the proper length and who measures the contracted length?
This is correct.

3. Sep 6, 2007

### Staff: Mentor

Good. This is the length of the moving ship 2 as measured by ship 1.
How did you do this? Do moving objects measure to be shorter or longer compared to their rest lengths?

Oops: Gokul43201 beat me!

4. Sep 6, 2007

### tacosareveryyum

Okay, I am going in circles here. Isn't a measurement of length of the moving second ship going to yield a shorter length than the measurement made in the frame of the ship.

5. Sep 6, 2007

### tacosareveryyum

Okay so the second ship should be measured to be 12.50 m as measured in its own rest frame.

6. Sep 6, 2007

Exactly.

Much better.

7. Sep 6, 2007

thanks!