Question

in case a, an object is moving in a straight line at a constant speed of 9.8 m/s. in case b, an object is moving in a straight line with a constant acceleration of 9.8 m/s². which of the following statements is true?

a nonzero net external force acts on the object in case a only.

a nonzero net external force acts on the object in both cases.

a nonzero net external force acts on the object in neither case.

a nonzero net external force acts on the object in case b only.

Explanation:

Step1: Recall Newton's second - law

Newton's second - law is $F = ma$, where $F$ is the net external force, $m$ is the mass of the object, and $a$ is the acceleration.

Step2: Analyze Case A

In Case A, the object is moving at a constant speed. So, the acceleration $a = 0$. According to $F=ma$, when $a = 0$, $F=0$ (assuming non - zero mass $m$).

Step3: Analyze Case B

In Case B, the object has a non - zero constant acceleration $a=9.8\ m/s^{2}$. Since $m
eq0$ and $a
eq0$, from $F = ma$, we have $F
eq0$.

Answer:

D. A nonzero net external force acts on the object in Case B only.