A vector quantity can only be completely described when ……… and …………are mentioned.

1. Analyze the question

The question asks for the two essential components required to fully define a vector quantity in physics.

2. Explain the concept

In physics, physical quantities are categorized into two main types:

• Scalar Quantities: These are quantities that have only magnitude (size or numerical value) but no direction. Examples include distance, speed, mass, and time.
• Vector Quantities: These are quantities that require both magnitude and direction to be fully described. If you only provide the magnitude, the description is incomplete. For example, if you say "a car is moving at 50 km/h," you have given the speed (scalar). If you say "a car is moving at 50 km/h due North," you have given the velocity (vector).

3. Show the solution

• Option A (Magnitude and motion): "Motion" is a general term for change in position, not a specific requirement for defining a vector.
• Option B (Magnitude and direction): This matches the definition of a vector quantity perfectly. A vector needs a value (magnitude) and a path/orientation (direction).
• Option C (Distance and specified displacement): Distance is a scalar, and displacement is a vector. This does not define a vector quantity in general.
• Option D (Moment and momentum): These are both examples of vector quantities, not the components required to define them.

4. Identify the answer

The correct option is B.

5. Exam Tip

To remember the difference, use the acronym "SMAD":

• Scalar = Magnitude
• Vector = Magnitude + Direction

Whenever you see a question about vectors, immediately look for the pair "Magnitude and Direction." If you see them together, that is almost certainly your answer!