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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Rest and Motion Kinematics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Rest and Motion Kinematics

Choose the correct statements:

Choose the correct statements:

Options

  1. AOver a time interval, the average velocity of a particle travelling on a straight line is zero. It is possible that its instantaneous velocity is never zero during this interval. (Infinite accelerations are not permitted.)
  2. BOver a time interval, the average velocity of a particle is zero. It is possible that its instantaneous velocity is never zero during this interval.
  3. CThere can be a situation where \left|\dfrac{d\vec{v}}{dt}\right| \neq 0whilewhile\dfrac{d}{dt}|\vec{v}| = 0..
  4. DIn a given time interval, the average speed of a particle is never smaller than the magnitude of its average velocity.

Correct answer

D. In a given time interval, the average speed of a particle is never smaller than the magnitude of its average velocity.

Step-by-step solution

For statement (1): Since the particle moves on a straight line and its average velocity is zero, its net displacement is zero. This implies the particle must have reversed its direction to return to the starting point. For a continuous velocity-time graph (as infinite acceleration is not permitted), the velocity must pass through zero. Thus, statement (1) is incorrect.

For statement (2): If a particle moves in a closed 2D or 3D loop (such as a circle) and returns to its starting point, its net displacement is zero, making the average velocity zero. However, its instantaneous velocity vector can have a non-zero magnitude (speed) throughout the motion. Thus, statement (2) is correct.

For statement (3): \left|\dfrac{d\vec{v}}{dt}\right|representsthemagnitudeoftotalacceleration,whilerepresents the magnitude of total acceleration, while\dfrac{d}{dt}|\vec{v}|representstherateofchangeofspeed(tangentialacceleration).Inuniformcircularmotion,thespeedisconstant,meaningrepresents the rate of change of speed (tangential acceleration). In uniform circular motion, the speed is constant, meaning\dfrac{d}{dt}|\vec{v}| = 0.However,thedirectionofvelocitychangescontinuously,resultinginanon−zerocentripetalacceleration,meaning∣dv⃗dt∣≠0. However, the direction of velocity changes continuously, resulting in a non-zero centripetal acceleration, meaning \left|\dfrac{d\vec{v}}{dt}\right| \neq 0. Thus, statement (3) is correct.

For statement (4): The total distance traveled by a particle is always greater than or equal to the magnitude of its net displacement. Dividing both by the same time interval, the average speed is always greater than or equal to the magnitude of the average velocity. Thus, statement (4) is correct.
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