If Velocity Is Constant, Then Acceleration Is What?

Answer

Choose (a) zero.

Acceleration is the time derivative of the velocity vector:

$$\vec a=\frac{d\vec v}{dt}.$$

If $\vec v$ is constant, neither its magnitude nor its direction changes, so $d\vec v/dt=\vec 0$. Therefore the acceleration is zero. Option (b) is false because a nonzero constant acceleration would make velocity change with time. Option (c) is too broad: zero is the specific constant value. Option (d) is unnecessary because the stated condition already determines the result.

Constant speed alone would not be enough. In uniform circular motion, speed is constant while the velocity direction changes, producing centripetal acceleration. The question says constant velocity, not merely constant speed.