Question

A particle moves with uniform velocity. Which of the following statements about the motion of the particle is true?
A) Its speed is zero.
B) Its acceleration is zero.
C) Its acceleration is opposite to the velocity.
D) Its speed may be variable.

Answer 1

Hint: We need to understand what is the correct definition of the uniform velocity in order to understand the dependence of other physical quantities such as the speed and the acceleration on the velocity of the moving particle to solve this problem.

Complete answer:
The motion of a particle involves many physical quantities which include distance, displacement, speed, velocity and acceleration. We are given a particle which moves with a uniform velocity. We need to understand what the velocity of a particle means in order to find the relation between the speed and the acceleration of the particle.
The velocity is defined as the rate of change of displacement of a body. It is the physical quantity which is dependent on both the direction of the motion and the magnitude of the speed. The speed is the scalar quantity which gives the magnitude of rate of change of position. The velocity is a special case of speed which involves the direction. For velocity to be uniform, the motion should have a constant speed and a constant direction.
The acceleration is the rate of change of velocity. Any change in velocity – with magnitude or direction – will result in acceleration.
Therefore, in the given case, there exists no acceleration or speed variation. Also, the speed will not be zero.
The acceleration of the particle in motion will be zero during a uniform velocity.

Hence, the correct answer is option B.

Note:
The uniform velocity and the uniform speed should not be confused. The uniform speed requires only the magnitude to be constant throughout as in a uniform circular motion whereas the uniform velocity requires the direction also to be constant as in a straight line motion.