Which of the following must always be true ? I. If an object's acceleration is constant, then it must move in a striaght 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.

Which of the following must always be true ? I. If an object's accele

1.	Which of the following must always be true ? I. If an object's acceleration is constant, then it must move in a striaght 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.
Answer» I and II only I and III only II only III only Solution :Statement I is false since a PROJECTILE experiencing only the CONSTANT acceleration due to gravity can TRAVEL in a parabolic trajectory. Statement II is true : Zero acceleration means no change in speed (or DIRECTION). Statement III is false : An object whose speed remains constant but whose velocity vector is CHANGING direction is accelerating .

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Which of the following must always be true ? I. If an object's acceleration is constant, then it must move in a striaght 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.

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