Question

Which of the following is a vector quantity?

A) Speed

B) Displacement

C) Mass

D) Time

Answer 1

Hint: We are given four quantities in the physical world. We have to consider each of them and their definitions to predict whether it is a vector or scalar quantity. The vector quantity has both direction and magnitude, whereas, the scalar has magnitude only.

Complete answer:

We know that the vector quantities are those physical quantities which are defined by both direction and magnitude. The scalar quantities are those which are defined by magnitude alone. Let us see with each of the given physical quantities to state which among them is a vector quantity.

1. Speed: It is defined by the rate of change of distance. We know that the speed is defined by a quantity that is not vector in nature, i.e., the distance. The distance is the length of the path travelled by the body. It doesn’t care about any direction. From this we can understand the speed is also a scalar quantity.

2.Displacement:The displacement is the shortest path between two points which  has magnitude as well as direction. It has the magnitude of shortest distance  from A to B joined by a straight line. Also, between two points A and B the displacement will not change, it has a fixed magnitude. It is because the displacement is defined along a direction, i.e.,  straight from A to B. From this we can conclude that displacement is a vector quantity.

3.Mass: It is the quantity which denotes how much a matter consists of. It is independent of direction as the mass remains constant in every context. Therefore, it is a scalar quantity.

4.Time: It is a physical quantity which denotes the duration. It can never be reversed or manipulated in any other direction. It is always unidirectional and therefore, doesn’t have a direction element during the calculations. It is not a vector quantity either.

We have got the vector quantity from the listed quantities as the displacement.

So, the correct answer is “Option B”.

Note:  Almost all the physical quantities which are scalar have vectors to be comparable with. The displacement in case of the distance, the weight in case of the mass and the velocity in case of the speed are a few among them. We should be careful in dealing with these terms.