Define velocity in words.
A constant driving force of $2400\,\text{N}$ acts on a car of mass $1200\,\text{kg}$. The car starts from rest and travels in a straight line on a horizontal road. Take the resistive forces on the car to be negligible. Calculate the acceleration of the car.
On Fig. 3.1, sketch a graph to show how the velocity $v$ of the car varies with time $t$ during the first $20\,\text{s}$ of motion. Label this line A.
In practice, a resistive force from air resistance acts on the car in (b). This resistive force rises with speed until, at time $t = 12\,\text{s}$, it becomes equal in magnitude to the driving force. On Fig. 3.1, sketch a second line to show how the car’s velocity $v$ varies with time $t$ during the first $20\,\text{s}$ of motion. Label this line B.
At time $t = 20\,\text{s}$, the driving force is increased to $3000\,\text{N}$ and then kept at this value. Describe how the car’s velocity changes after this increase in driving force.