Question

18 mark for review the acceleration a as a function of time t for a foam ball released from rest near the surface of earth is shown in the graph. the ball experiences a resistive force from the air. the magnitudes of the resistive force at times t1 = 0.1 s and t2 = 0.8 s are f1 and f2, respectively. which of the following correctly compares f1 and f2? a f1 = f2 b f1 > f2 c f2 > f1 = 0 d f2 > f1 > 0

Explanation:

Step1: Apply Newton's second - law

According to Newton's second - law $F_{net}=ma$, and $F_{net}=mg - F_{res}$, so $ma = mg - F_{res}$, and $F_{res}=mg - ma$.

Step2: Analyze acceleration values

From the graph, at $t_1 = 0.1\ s$, the acceleration $a_1$ is relatively large. At $t_2=0.8\ s$, the acceleration $a_2$ is relatively small. Since $m$ and $g$ are constant ($m$ is the mass of the ball and $g$ is the acceleration due to gravity).

Step3: Compare resistive forces

Using $F_{res}=mg - ma$, when $a$ is larger, $F_{res}$ is smaller. Since $a_1>a_2$, we have $F_10$ and $F_2>0$.

Answer:

D. $F_2 > F_1>0$