WAEC Physics 2012 Paper

Concept:Pressure is defined as force acting per unit area.Explanation:Pressure is given by:$$\text{Pressure} = \frac{\text{Force}}{\text{Area}}$$Force is the product of mass and acceleration:$$\text{Force} = \text{mass} \times \text{acceleration}$$Substituting this into the pressure formula gives:$$\text{Pressure} = \frac{\text{mass} \times \text{acceleration}}{\text{Area}}$$Now express each quantity in SI base units:Mass is in kg, acceleration is in $\text{m s}^{-2}$, and area is in $\text{m}^2$.Thus:$$\text{Pressure} = \frac{\mathrm{kg} \times \mathrm{m\,s}^{-2}}{\mathrm{m}^2}$$Simplifying the metre units:$$\frac{\mathrm{m}}{\mathrm{m}^2} = \mathrm{m}^{-1}$$So the derived unit of pressure is:$$\mathrm{kg\,m^{-1}s^{-2}}$$Answer:The correct option is B: $\mathrm{kg\,m^{-1}s^{-2}}$.