# HW3 - Physics 215 Spring 2016 Homework#3 1 A particle...

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Physics 215 – Spring 2016 Homework #3 1.A particle having a speed of 0.92 c has a momentum of 10ିଵ଺݇݃ ∙ ݉ ݏ⁄ .What is its mass a) in kg, and b) in MeV /c2 units? 2. Calculate the momentum, kinetic energy, and total energy of an electron traveling at a speed of (a) 0.20c, and (b) 0.90c. 3. At what energy does an electron become “relativistic”? Consider electrons with kinetic energies of 50 eV, 50 keV, and 50 MeV. For each case, calculate the momentum of the electron first using the non-relativistic formula for kinetic energy, and then using the correct relativistic formulas. Express the momentum in units of eV/c, or keV/c, or MeV/c (whichever is appropriate). (The rest energy of an electron is 0.511 MeV.) Compare your answers for each case. When is it important to use the relativistic formulas? 4. The total energy of a body is found to be twice its rest energy. How fast is it moving with respect to the observer? 5. A muon has a mass of 106 MeV /c2. Calculate the speed, momentum, and total energy of a muon with a kinetic energy of 200 MeV.6. An Ωିparticle has rest energy 1672 MeV and mean lifetime 8.2 x 10ିଵଵs. It is created and decays in a particle track detector and leaves a track 24 mm long. What is the total energy of the Ωିparticle?