1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relativity With velocity of objects moving in different fram

  1. Jun 2, 2017 #1
    1. The problem statement, all variables and given/known data
    1. i)A police spaceship P is chasing another spaceship A. Both ships have velocities βP = βA = 3c/5 as measured along the x axis in the Solar System reference frame O. The police ship is a distance L = 1 light-second (i.e. the distance travelled by light in one second) behind ship A. What is this distance in the frame of the police ship O′?

      ii)The police ship fires a missile at speed βM′ = 4c/5 at time t′ = 0 and position x′ = 0 as measured in the police spaceship frame O′. When and where does the missile reach ship A, as measured in frame O?

      Really I am interested to see If my solution is correct and if not where i went wrong.
    2. Relevant equations
    t′ =γ(ct−βx), x′ =γ(x−βct), y′ =y, z′ =z And all inverses as well

    D = s * t
    γ = 5/4 (if you calculate it)

    3. The attempt at a solution
    i) I believe that length contraction is a valid way to proceed and in the frame of the solar system since it is moving relative to observer it will be not proper length while in frame O' it is proper length hence in O' it should be 5/4 light second

    ii) Since moving at same speed and using addictive relativistic formula the relative velocity is zero between the two objects and in frame O' they are separated at 5C/4 and the rocket being fired relative to police spaceship is 4c/5 hence the time taken in frame O' , t' = 25/16 and x' = 5c/4

    Using the inverse lorentz equation (to convert position in frame O' to O) we see that x = 175c/64 and t = 185/64

    Please could anyone let me know if the above is correct?
  2. jcsd
  3. Jun 2, 2017 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Looks good except for the lack of units on your answers.

    You could check your answers by solving the problem in the unprimed frame by calculating the speed of the missile in the unprimed frame and then solving for when it'll catch up to the moving ship A.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted