Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Spontaneous disintegration in classical mechanics

  1. Jan 21, 2012 #1
    Could someone demonstrate to me how in Landau's Mechanics book, he gets from equation (16.5)

    tan θ = (v_0 sin θ_0) / (v_0 cos θ_0 + V)

    to equation (16.6)

    cos θ_0 = -(V/v_0) sin^2 θ ± cos θ √[1 - (V/v_0)^2 sin^2 θ]

    I am using the quadratic formula, and the first term on the right comes out fine, but I can't get the second term.

  2. jcsd
  3. Jan 25, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    It worked out for me. What did you get for the quadratic you needed to solve and what did you get for the discriminant?
  4. Jan 25, 2012 #3
    Oh boy, I remember doing that one
    a lot of the equations in those books are quite annoying (not 'hard' exactly) to arrive at.
    you just need to make use of [itex]sin=\sqrt{1-cos^2}[/itex]

    there are a lot more tricky ones later on though so good luck :devil:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook