I need help with two of these questions. 1. An electron is travelling at 0.866c, with respect to the face of a television picture tube. What is the value of its relativistic momentum to the tube? Im not goin to post every single step but i'll post my answer. p=mv/sqrt(1-v^2/c^2) p=9.11 x 10^-31 x (0.866 x 3.00 x 10^8)/sqrt(0.250044) p=4.74 x 10^-22 Thats the answer i get but in my book, they have 1.58 x 10^-30. 2. The electron and positron each have a rest mass of 9.11 x 10^-31 kg. In a certain experiment, an electron and positron collide and vanish, leaving only electromagnetic radiation after the interaction. Each particle is moving at a speed of 0.20c relative to the laboratory before the collision. Determine the energy of the electromagnetic radiation. First of all do i have to solve this question like a collision problem, if i do there is no after situation. Anyways i think i have to solve for Ek. So Et=Ek + Erest Et=mc^2/sqrt(1-v^2/c^2) Et=9.11 x 10^-31 x (3.00 x 10^8)^2/sqrt(0.96) Et=8.37 x 10^-14 Erest = 8.2 x 10^-14 Ek= 8.37 x 10^-14 - 8.2 x 10^-14 Ek= 1.7 x 10^-15 But this answer isnt right. In my book they have 0.615 MeV and when i convert my answer to that i dont get that answer. So what did i do wrong ,cant anyone help me please.