1. The problem statement, all variables and given/known data An electron traveling at a speed of 6.0 x10^7 m/s. strikes the target of an x-ray tube. Upon impact, the electron decelerates to 1/4th of its original speed, emitting an x-ray in the process. What is the wavelength of the x-ray photon? 2. Relevant equations I think I'm suppose to use the formula E=hf (eqn 1) and v=lambda*f (eqn 2) 3. The attempt at a solution I manipulated both equations (eqn 1 and eqn 2) to get the formula E=(h*v)/(lambda), but that leaves me with two unknowns..when all I want is lambda to be the only unknown. I'm not sure how I would find the energy...and I'm not sure if I'm even using the correct formulas. Hopefully I'm on the right track???