The motion of a bus is represented by a straight-line segment on a velocity-time graph from (0,4)(0,4)(0,4) to (10,19)(10,19)(10,19), where time is measured in seconds and velocity in m s−1^{-1}−1.
State the modelling assumption represented by the straight-line segment.
Find the modelled acceleration.
Give one reason why the graph may not represent the bus's motion exactly.