text: The above answer is not quite right.  In relativistic mechanics, momentum is defined as:\n\n  p = g * m * v\n\nwhere \ng = 1/sqrt(1-(v/c)^2),\nv is the velocity of the object in question (relative to some observer), \nc is the speed of light, \nand m is the rest mass of the moving object.  \n(Strictly speaking, both p and v are vector quantities.)\n\nFor |v|<<c, g is approximately equal to 1, and the relativistic momentum approaches m*v, the classical Newtonian value of the momentum.  \n\nIn the case at hand, g = 1/sqrt(1-0.15^2) = 1.01144, so the relativistic momentum of the electron is 1.01144 times the classical value (i.e., 1.144% higher than just m*v).