The correct option is **C. Force**. ### Detailed Explanation In the International System of Units (SI), quantities are classified into two main categories: base quantities and derived quantities. 1. **Base Quantities**: These are the fundamental physical quantities from which other quantities can be derived. The seven base quantities in the SI system are: - Length (meter, m) - Mass (kilogram, kg) - Time (second, s) - Electric current (ampere, A) - Thermodynamic temperature (kelvin, K) - Amount of substance (mole, mol) - Luminous intensity (candela, cd) 2. **Derived Quantities**: These are quantities that are derived from the base quantities through mathematical relationships. They are expressed in terms of the base quantities. **Force** is a classic example of a derived quantity. It is defined by Newton's second law of motion, which states that force is the product of mass and acceleration. The formula for force is given by: \[ F = m \cdot a \] where: - \( F \) is the force measured in newtons (N), - \( m \) is the mass measured in kilograms (kg), - \( a \) is the acceleration measured in meters per second squared (m/s²). In SI units, the newton (N) can be expressed in terms of base units as: \[ 1 \, \text{N} = 1 \, \text{kg} \cdot \text{m/s}^2 \] This shows that force is derived from the base quantities of mass and length (and time, through acceleration). ### Why the Other Options Are Incorrect - **A. Length**: Length is a base quantity in the SI system. It is measured in meters (m) and does not depend on any other quantities for its definition. - **B. Mass**: Mass is also a base quantity in the SI system. It is measured in kilograms (kg) and is fundamental to the definition of other quantities, such as force. - **D. Time**: Time is another base quantity in the SI system, measured in seconds (s). Like length and mass, it is fundamental and does not derive from other quantities. ### Common Pitfalls - Students often confuse derived quantities with base quantities. Remember that derived quantities are formed from combinations of base quantities. - It’s important to understand the definitions and relationships between these quantities, especially in the context of physics problems involving force, motion, and other dynamics. ### Revision Summary - **Base quantities** in SI include length, mass, time, electric current, temperature, amount of substance, and luminous intensity. - **Derived quantities** are formed from base quantities; force is derived from mass and acceleration. - The formula for force is \( F = m \cdot a \), and it is measured in newtons (N). - Remember the distinction between base and derived quantities to avoid confusion in physics problems.