1. The problem statement, all variables and given/known data By expanding Krel / Kcl in powers of (v/c)^2, estimate the value of v/c for which Krel differs from Kcl by 10%. 2. Relevant equations Kcl = classical Kinetic Energy = 1/2 m0 v^2 Krel = relative Kinetic Energy = (y-1) (m0 c)^2 3. The attempt at a solution I did a binomial expansion wherein x = (v/c)^2 and n = -1/2 The result is... [1 - (v/c)^2]^(-1/2) = 1 + 1/2(v/c)^2 so If I plug this value into the Lorentz factor of Krel, I can equate K rel to the Kcl equation. But at which step of this expansion can I apply the 10% difference? Do I need to set up an equation wherein Krel = 11/10 (Kcl)? Thanks!