Halliday, Resnick & Walker — Motion in Two and Three Dimensions: Problem 14

A proton initially has \(\vec{v} = 4.0\hat{i} - 2.0\hat{j} + 3.0\hat{k}\) and then \(4.0\text{ s}\) later has \(\vec{v} = -2.0\hat{i} - 2.0\hat{j} + 5.0\hat{k}\) (in meters per second). For that \(4.0\text{ s}\), what are (a) the proton's average acceleration \(\vec{a}_{\text{avg}}\) in unit-vector notation, (b) the magnitude of \(\vec{a}_{\text{avg}}\), and (c) the angle between \(\vec{a}_{\text{avg}}\) and the positive direction of the \(x\) axis?