Which of the following must always be true? I. If an object's acceleration is constant, then it must move in a straight line. II. If an object's acceleration is zero, then its speed must remain constant. III. If an object's speed remains constant, then its acceleration must be zero.
Correct answer: C. II only
- A. I and II only
- B. I and III only
- C. II only
- D. III only
Explanation
Option C is correct as only statement (ii) is true. Zero acceleration implies there is no change in speed. On the other hand statements (i) and (iii) are incorrect. Statement (i) is false as projectile motion has constant acceleration but it does not have a straight path. Statement (iii) is false as in circular motion the speed of the object remains the same, but its acceleration is not zero.
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