A proton is projected in the positive $x$ direction into a region of a uniform electric field $\mathbf{E}=-6.00 \times 10^{5} \hat{\mathbf{i}} \mathrm{N} / \mathrm{C}$ at $t=0 .$ The proton travels 7.00 $\mathrm{cm}$ before coming to rest. Determine (a) the acceleration of the proton, (b) its initial speed, and (c) the time at which the proton comes to rest.