Brakes

The braking efficiency of a passenger car is required to stop at 12.5 m at an initial speed of 40 km/h. What is the acceleration braking by brakes?

Correct answer:

a =  -4.9383 m/s²

Step-by-step explanation:

$$\begin{gathered} v_1=40\text{km/h}\to \text{m/s}=40:3.6\text{m/s}=11.11111\text{m/s} \\ {v}_2=0\text{m/s} \\ s=12.5\text{m} \\ v=\frac{v_1+v_2}{2}=\frac{\frac{100}{9}+0}{2}=\frac{50}{9}\doteq 5.5556\text{m/s} \\ t=s/v=12.5/5.5556=\frac{9}{4}=2.25\text{s} \\ a=\frac{v_2-v_1}{t}=\frac{0-\frac{100}{9}}{\frac{9}{4}}=-\frac{400}{81}{\text{m/s}}^2=-4.9383{\text{m/s}}^2 \end{gathered}$$

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