Which of the following describes an object with $a=0$?

• A. Changing direction while maintaining $v$
• B. Slowing down to a stop
• C. Moving at a constant $v$
• D. Speeding up in a straight line

Answer: (C)

Verified step by step guidance

1. Understand that acceleration \(a\) is defined as the rate of change of velocity \(v\) with respect to time, mathematically expressed as \(a = \frac{d v}{d t}\).
2. Recognize that if acceleration \(a = 0\), it means the velocity \(v\) is not changing over time; both its magnitude (speed) and direction remain constant.
3. Analyze each option: Changing direction while maintaining \(v\) implies velocity direction changes, so acceleration is not zero because velocity vector changes.
4. Slowing down to a stop means the speed is decreasing, so acceleration is not zero because velocity magnitude changes.
5. Speeding up in a straight line means velocity magnitude increases, so acceleration is not zero; only moving at a constant velocity \(v\) means acceleration is zero.