Question

a. acceleration and mass are directly proportional. b. force and acceleration are unrelated. c. acceleration increases as force increases, if mass stays the same. d. force decreases as acceleration increases, if mass stays the same.

Explanation:

According to Newton's second - law of motion $F = ma$ (where $F$ is force, $m$ is mass and $a$ is acceleration). When mass $m$ is constant, $F$ and $a$ are directly proportional, i.e., $a=\frac{F}{m}$. So, if mass stays the same, force increases as acceleration increases and vice - versa.

Answer:

D. Force decreases as acceleration decreases, if mass stays the same.