Question

Distinguish between uniform velocity and variable velocity.
A. Uniform velocity changes with time, while variable velocity doesn’t change with respect to time.
B. Uniform velocity is scalar, while variable velocity is vector.
C. Uniform velocity doesn’t change with time, while variable velocity changes with respect to time
D. Uniform velocity is vector, while variable velocity is scalar.

Answer 1

Hint: When the motion of a body is in such a way that it has equal displacements in equal intervals of time, the body is said to be in uniform velocity. It will be a constant value. When the velocity of the body is not constant with respect to time, its velocity is called variable velocity.

Complete step by step answer:
Velocity is defined as the change in position of a body in one unit of time or the displacement of the body in one unit of time.
Since velocity changes its position in one unit of time, it has a specific direction. Hence, it is a vector quantity. The SI unit of velocity is $m{{s}^{-1}}$.
When the motion of a body is in such a way that it has equal displacements in equal intervals of time, the body is said to be in uniform velocity. And the velocity of the particle is simply the ratio of the displacement in the given time interval to the time interval.
Suppose a body is moving with a uniform velocity. Consider an interval of time t. Let the magnitude of displacement of the body the interval of time t be s. As per the definition of uniform velocity, for every time interval equal to t, the displacement of the body will be s. Therefore, the velocity of the body is $\dfrac{s}{t}$ and this will be a constant value.
Hence, we get that the velocity of a body moving with uniform velocity is constant with time.
When the velocity of the body is not constant with respect to time, its velocity is called variable velocity.
Therefore, uniform velocity doesn’t change with time, while variable velocity changes with respect to time
Hence, the correct option is C.

Note: The options B and D are incorrect because both, uniform velocity and variable velocity are vector quantities.
Since uniform velocity and variable velocity are types of velocities, both of them have to be vectors quantities.