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!

Homework Help: Modern Physics Question (Velocity-Addition)

  1. Oct 13, 2012 #1
    The problem statement, all variables and given/known data
    Spacecraft 1 is launched from the surface of the Earth with a velocity of 0:6c (Earth
    RF) at an angle of 50

    above the horizontal +x axis. Spacecraft 2 is moving with a
    velocity of 0:7c (Earth RF) in the x direction towards Spacecraft 1. Determine the
    velocity and speed of Spacecraft 1 as measured by the pilot of Spacecraft 2.

    The attempt at a solution
    I'm trying to solve this and I'm stuck a bit so far all ive got is that
    Vs1e (velocity of space craft 1 respect to earth) = 0.6cos50(c)
    Vs2e = -0.7c

    they want Vs1s2 = Vs1e + Ves2/ 1 + Vs1e (Ves2)/c^2

    I'm stuck because I don't know what "Ves2" would be...

    Thanks in advance
  2. jcsd
  3. Oct 14, 2012 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF;
    I can't tell either ... I hate subscripts.

    In the E frame:
    Craft 1 has an x and a y component.
    Craft 2 only has an x component.

    Use the formula on each component to find the relative velocity of frames 1 and 2.
  4. Oct 14, 2012 #3
    Lol Thanks,

    So should I first do the formulas for the x components and the y components and then combine it..and the hypotenuse would be the answer?
  5. Oct 14, 2012 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Well... one of the directions does not matter.
    Remember the derivation of time dilation you did a while ago - only one of the directions counted for that too.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook