22. which option best describes the average acceleration from 40 to 70 s? a. it is negative and smaller in…

Explanation:

Step1: Recall acceleration formula

Acceleration $a=\frac{\Delta v}{\Delta t}$, where $\Delta v = v_f - v_i$ and $\Delta t=t_f - t_i$.

Step2: Determine $v_i$, $v_f$, $t_i$ and $t_f$ from graph

At $t_i = 40\ s$, $v_i\approx240\ m/s$. At $t_f = 70\ s$, $v_f\approx240\ m/s$. So $\Delta t=70 - 40=30\ s$ and $\Delta v=240 - 240 = 0\ m/s$.

Step3: Calculate average - acceleration

$a=\frac{\Delta v}{\Delta t}=\frac{0}{30}=0\ m/s^2$. Initially (from $t = 0$ to $t = 10\ s$), the velocity is increasing, so the initial acceleration is positive. Since the average acceleration from $40$ to $70\ s$ is $0$, it is positive (compared to negative values) and smaller in magnitude than the non - zero initial acceleration.

Answer:

c. It is positive and smaller in magnitude than the initial acceleration.