(i)[4]
As the lorry travels from the foot to the top of the hill at constant speed, the resisting force on it is $800\,\text{N}$ and the work done by the driving force is $2800\,\text{kJ}$. Find $\alpha$.
(ii)[4]
During the return trip the lorry has speed $20\,\text{m s}^{-1}$ at the top of the hill. As it moves downhill, the work done by the driving force is $2400\,\text{kJ}$ and the work done against the resistance to motion is $800\,\text{kJ}$. Find the speed of the lorry at the bottom of the hill.