(a)[1]
Define acceleration in words.
(b(i))[2]
Calculate the time needed for the train to increase its speed from $15\text{ m s}^{-1}$ to $28\text{ m s}^{-1}$.
(b(ii))[2]
Calculate the force needed for this train to have an acceleration of $1.1\text{ m s}^{-2}$.
(b(iii))[1]
Explain why the force on the train from the motors is larger than the value worked out in (ii).