Determine the final velocity of a proton that has an initial velocity of 2.15x10^5 m/s, and then is accelerated uniformly in an electric field at the rate of -1.10x10^12 m/s2 for 1.20x10^-7 s.

Since the acceleration is negative, the speed gets reduced by an amount

deltaV = |a|*t = 1.1*10^12*1.2*10^-7 = 1.32*10^5 m/s
That makes the final speed 0.83*10^5 m/s