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 units. Examples of derived quantities include: - Area (square meters, m²) - Volume (cubic meters, m³) - Speed (meters per second, m/s) - Force (newton, N) ### Why Force is a Derived Quantity Force 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 in newtons (N), - \( m \) is the mass in kilograms (kg), - \( a \) is the acceleration in meters per second squared (m/s²). From this formula, we can see that force is derived from the base quantities of mass and acceleration. Since acceleration itself is derived from the change in velocity over time (which involves length and time), force is indeed a derived quantity. ### Why the Other Options are Incorrect - **A. Time**: Time is a base quantity in the SI system, measured in seconds (s). It is fundamental and not derived from other quantities. - **B. Mass**: Mass is also a base quantity in the SI system, measured in kilograms (kg). Like time, it is a fundamental quantity and not derived from others. - **D. Length**: Length is another base quantity in the SI system, measured in meters (m). It is fundamental and serves as a basis for deriving other quantities. ### Common Pitfalls - Students often confuse derived quantities with base quantities, especially when they are familiar with the concepts of force and motion. Remember that derived quantities are formed from combinations of base quantities. - It’s important to understand the relationships between different physical quantities and how they are interrelated through formulas. ### Revision Summary - **Base quantities** in the SI system include time, mass, and length; they are fundamental and not derived. - **Derived quantities** are formed from base quantities; force is a prime example, derived from mass and acceleration. - The formula for force is \( F = m \cdot a \), illustrating its dependence on base quantities. - Always differentiate between base and derived quantities to avoid confusion in physics problems.