If an object moves with constant velocity then which one of the following statements is NOT correct?
- A.Its motion is along a straight line
- B.Its speed changes with time.
- C.Its acceleration is zero
- D.Its displacement increases linearly with time
Correct answer
Explanation
The correct answer is B, Its speed changes with time. Constant velocity means both the speed and the direction stay the same, so the speed cannot change.
Velocity is a vector: it has a magnitude, the speed, and a direction. If the velocity is constant, neither part changes. A body moving with constant velocity therefore travels in a straight line at a steady speed, covers equal displacements in equal intervals of time and has no acceleration. By Newton's first law, the net force on it is also zero.
A is wrong: this statement is correct, because a constant direction means the path is a straight line.
C is wrong: this statement is correct, because acceleration is the rate of change of velocity, and an unchanging velocity gives zero acceleration.
D is wrong: this statement is correct, because displacement equals velocity × time, which grows in direct proportion to time.
Exam tip: uniform circular motion has constant speed but changing velocity; constant velocity always means straight-line motion with zero acceleration.
Practice Questions
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- C.barometer
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- C.200-20,000 Hz only
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