Minimum energy a proton must have to penetrate.... 1. The problem statement, all variables and given/known data Determine the minimum energy that a proton must have to penetrate 30 cm of tissue, the approximate thickness of the human body. 2. Relevant equations I used R=[(E/9.29)^1.8]1.11x10^-3 but I'm not sure if this is correct. 3. The attempt at a solution R=[(E/9.29)^1.8]1.11x10^-3 30 cm=3 mm 3mm=[(E/9.29)^1.8]1.11x10^-3, then I divided by 1.11x10^-3 to get 27027.70mm=(E/9.29)^1.8 Then I took a root to the 1.8 power and got 80.64mm=E/9.29 I then multiplied by 9.29 to get 749 mEV. Seems a bit high. Wasn't sure about units or if I even used the correct formula? Thanks for your help!