SAT Subject Physics Practice Question 151: Answer and Explanation
14. A particle whose rest energy is E is traveling at a speed of c. What is the particle’s kinetic energy?
Correct Answer: D
Because v is close to c, the particle is relativistic, so it would be incorrect to use the formula KE = mv2. Instead, we must use the formula KE = (γ – 1)mc2. Since v = c, the relativistic factor is
So, the kinetic energy of this particle is