First, calculate the driving force (DF) using the power formula:

\(P = F \cdot v\), where \(P = 400 \text{ W}\) and \(v = 4 \text{ m s}^{-1}\).

\(F = \frac{P}{v} = \frac{400}{4} = 100 \text{ N}\).

For uphill motion, apply Newton's second law:

\(DF - 80g \sin 2^{\circ} = 80a\).

Substitute \(DF = 100 \text{ N}\) and \(g = 9.8 \text{ m s}^{-2}\):

\(100 - 80 \times 9.8 \times \sin 2^{\circ} = 80a\).

Calculate \(\sin 2^{\circ} \approx 0.0349\):

\(100 - 80 \times 9.8 \times 0.0349 = 80a\).

\(100 - 27.352 = 80a\).

\(72.648 = 80a\).

\(a = \frac{72.648}{80} \approx 0.9 \text{ m s}^{-2}\).

For downhill motion, apply Newton's second law:

\(DF + 80g \sin 2^{\circ} = 80a\).

\(100 + 80 \times 9.8 \times 0.0349 = 80a\).

\(100 + 27.352 = 80a\).

\(127.352 = 80a\).

\(a = \frac{127.352}{80} \approx 1.6 \text{ m s}^{-2}\).