1. The problem statement, all variables and given/known data An electron is accelerated to a speed that is 99 percent the speed of light, and is moving through a 2-km-long tunnel. The rest mass of the electron is 9.11*10^-31 kg. What is the mass of the electron at this speed? c= speed of light 2. Relevant equations t= (tsubscript(o))/ root(1-(v^2/c^2) L= Lsubscript(o)* root(1-0)= Lsubscript(o) p= (mv)/ root(1-0) = mv KE= ((mc^2)/ root(1-(v^2/c^2))-mc^2 3. The attempt at a solution I tried plugging the rest mass into the last equation on the top which gives me 9.11*10^-31/ root(1-((.99c)^2/c^2 which calculates out to 9.11*10^-31/ root(1-.9801) 9.11*10^-31/root(0.0199) 9.11*10^-31/0.14106736 =6.458*10^-30 I'm unsure if this is correct. It's listed as one of the answers but I don't know if I used the correct equation, so the fact that it's listed as an answer could be a trick. I also don't know how the 2km long tunnel plays into the equation. Please help!