using Relativistic mechanics Gamma = 1 / (Root (1/ v^2/c^2)) The target area in a lab in a straight line tube of 400 m long. 1 million radioactive particles are shot in this tube at (3/5) c . Half of them will arrive at the other end without decaying. To the observer moving with the particle: a) how long is the tube measured to be? shorter than 400m, i would think it's 400 / gamma = 400 / 1.25 = 320m b) what is the half life of the particles? is this as easy i think it is? t = D/ v = 400 / (3/5)c = 2.22 x 10^-6 s and thus half life is 1.11 x 10^-6 s c) What is the speed the tube is measured to move? in the opposite direction at (3/5)c?