1. Imagine a particle moving relative to the laboratory reference system at a rate of 0.050c. The particle emits an electron when it decays. The electron velocity is 0.80c, and the direction of electron velocity is the same as that of particle motion. Try to find the speed of the electron relative to the laboratory reference system.
2. In the S system, a rod with an original length of $l_0$ is placed along the x-axis and moves along the xx' axis at the speed u. If an S' system moves along the xx' axis relative to the S system at the speed v, what is the length of the rod measured in the S' system?
3. If the total energy of an electron is 5.0 MeV, calculate the kinetic energy, momentum and velocity of the electron.
