State Newton’s second law of motion in words.
A car with mass $850\,\text{kg}$ is towing a trailer in a straight line on a horizontal road. The change with time $t$ of the car’s velocity $v$ during part of the journey is shown in Fig. 2.2. Calculate the distance covered by the car from time $t = 0$ to $t = 10\,\text{s}$.
At time $t = 10\,\text{s}$, the resistive force on the car due to air resistance and friction is $510\,\text{N}$. The tow-bar tension is $440\,\text{N}$. For the car at time $t = 10\,\text{s}$: use Fig. 2.2 to calculate the acceleration.
Use your answer to find the resultant force acting on the car.
Show that the car’s engine exerts a horizontal force of $1300\,\text{N}$.
Determine the engine’s useful output power.
Calculate the distance covered by the car from time $t = 0$ to $t = 10\,\text{s}$.
At time $t = 10\,\text{s}$, the resistive force on the car due to air resistance and friction is $510\,\text{N}$. The tow-bar tension is $440\,\text{N}$. For the car at time $t = 10\,\text{s}$, use Fig. 2.2 to calculate the acceleration.
Use your answer to find the resultant force on the car.
Show that the engine exerts a horizontal force of $1300\,\text{N}$ on the car.
Determine the engine’s useful output power.
Shortly afterwards, the car in (b) is moving at constant speed and the tension in the tow-bar is $480\,\text{N}$. The tow-bar is a solid metal rod that obeys Hooke’s law. Some data for the tow-bar are given below: Young modulus of metal $= 2.2 \times 10^{11}\,\text{Pa}$, original length of tow-bar $= 0.48\,\text{m}$, cross-sectional area of tow-bar $= 3.0 \times 10^{-4}\,\text{m}^2$. Determine the extension of the tow-bar.
The driver of the car in (b) notices a pedestrian standing directly ahead in the distance. The driver sounds the car horn from time $t = 15\,\text{s}$ to $t = 17\,\text{s}$. The frequency of the sound heard by the pedestrian is $480\,\text{Hz}$. The speed of sound in air is $340\,\text{m s}^{-1}$. Use Fig. 2.2 to calculate the frequency of the sound emitted by the horn.