Brakes of a car

For the brakes of a passenger car to be effective, it is prescribed that a car be moving on a horizontal road at a speed of 40 km. A car must stop on the track 15.4 m. What is the deceleration of the car?

Correct answer:

a =  4.0083 m/s²

Step-by-step explanation:

$$\begin{gathered} v=40\text{km/h}\to \text{m/s}=40:3.6\text{m/s}=11.11111\text{m/s} \\ s=15.4\text{m} \\ s=\frac{1}{2}a{t}^2 \\ v=at \\ s=\frac{1}{2}a(v/a{)}^2 \\ 2s=v^2/a \\ a=v^2/(2\cdot s)=11.1111^2/(2\cdot 15.4)=4.0083{\text{m/s}}^2 \end{gathered}$$

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