Acceleration 4211

At the start of braking, the car had a speed of 72 km h at -1. It stopped on a track of 50 m. What was the acceleration, and how long did the braking last?

Correct answer:

a =  -4 m/s²
t =  5 s

Step-by-step explanation:

$$\begin{gathered} v_1=72\text{km/h}\to \text{m/s}=72:3.6\text{m/s}=20\text{m/s} \\ {v}_2=0\text{m/s} \\ s=50\text{m} \\ v=\frac{v_1+v_2}{2}=\frac{20+0}{2}=10\text{m/s} \\ t=s/v=50/10=5\text{s} \\ a=\frac{v_2-v_1}{t}=\frac{0-20}{5}=-4{\text{m/s}}^2 \end{gathered}$$

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