Question

Which of the following is not a vector quantity?
A. Retardation
B. Acceleration due to gravity
C. Average speed
D. Displacement

Answer 1

Hint:We know that vector quantities have both magnitude and direction but the scalar quantity has only magnitude but not direction. Retardation is also a negative acceleration. Displacement is a difference between the final position and initial position.

Complete answer:
To answer this question, let’s define vector and scalar quantities. We know that vector quantities have both magnitude and direction. Also, the scalar quantity has only magnitude but not direction. Let’s verify every given option as follows,

Retardation:
We know that retardation decreases the acceleration and it has the same value of acceleration but has the negative sign. Since the acceleration has the same direction as that of the force which produces the acceleration, it is a vector quantity.
We express the acceleration or retardation as follows,
$$\overrightarrow{a}={\displaystyle \frac{\overrightarrow{F}}{m}}$$
 Here, F is the force and m is the mass.

Acceleration due to gravity:
We know that the acceleration due to gravity always acts in the downward direction towards the ground. The value of acceleration due to gravity is . Thus, we see that the acceleration due to gravity has both direction and magnitude. Therefore, the option (B) is incorrect.

Average speed:
We know that velocity is the vector quantity. Also, the magnitude of velocity is known as average speed. It does not have direction. The velocity of the body at a given instant of time is referred to as average speed. It has magnitude but it has nothing to do with the direction.

Displacement:
Displacement is a vector quantity since it has both direction and magnitude. The distance between the two points is the scalar quantity. Therefore, the option (D) is incorrect.

So, the correct answer is option (C).

Note: To answer such type of questions, students can recall the formula in which the given quantity is used. If that formula of some physical quantity solely depends upon the direction of the given quantity, then the given quantity must be a vector quantity. In the above answer, to check whether the acceleration is scalar or vector, we used the formula for force. Since the force is vector quantity, the acceleration is also the vector quantity.