Essential University Physics: Volume 1 (3rd Edition)

We know that the time of flight of the protons is given as $t=\sqrt{\frac{2y}{g}}$ We plug in the known values to obtain: $t=\sqrt{\frac{(2)(1.2\times 10^{-6})}{9.8}}$ $t=4.94\times 10^{-4}s$ The speed of the protons is $v=\frac{x}{t}$ We plug in the known values to obtain: $v=\frac{1700}{4.949\times 10^{-4}}=3.4\times 10^6\frac{m}{s}$