Statics and Dynamics (Mechanics) accounts for up to 35% of marks in ECZ Grade 12 Physics (Paper 1 Multiple Choice & Paper 2 Structured Theory). Mastering equations of motion, Newton's laws, energy conservation, momentum, and power guarantees top distinction scores.
Mechanics Exam Strategy:
Always state the values of known variables ($u, v, a, t, s$) with SI units on your answer script before selecting the appropriate equation of motion!
1. Core Mechanics Formulas
Essential Mechanics Formulas:
- Linear Motion:
$$v = u + a t \qquad s = u t + \frac{1}{2} a t^2 \qquad v^2 = u^2 + 2 a s$$ - Newton's Second Law & Momentum:
$$F = m a \qquad p = m v \qquad \text{Impulse } I = F \Delta t = m(v - u)$$ - Work, Energy & Power:
$$\text{Work } W = F d \qquad E_k = \frac{1}{2} m v^2 \qquad E_p = m g h \quad (g = 9.8 \text{ or } 10\text{ m/s}^2)$$
$$\text{Power } P = \frac{W}{t} = F v$$
2. Worked Exam Example: Equations of Motion
Worked Example 1 (Paper 2 Dynamics):
A car of mass $1000\text{ kg}$ accelerates uniformly from rest to a velocity of $20\text{ m/s}$ in $5\text{ seconds}$.
(a) Calculate the acceleration of the car.
Known: $u = 0\text{ m/s}$, $v = 20\text{ m/s}$, $t = 5\text{ s}$.
$$a = \frac{v - u}{t} = \frac{20 - 0}{5} = 4\text{ m/s}^2$$
(b) Calculate the resultant accelerating force ($F$).
$$F = m a = 1000\text{ kg} \times 4\text{ m/s}^2 = 4000\text{ N}$$
(c) Calculate the distance ($s$) traveled during this 5-second period.
$$s = u t + \frac{1}{2} a t^2 = (0)(5) + \frac{1}{2}(4)(5^2) = 0 + 2(25) = 50\text{ meters}$$
(d) Calculate the kinetic energy ($E_k$) of the car at final velocity.
$$E_k = \frac{1}{2} m v^2 = \frac{1}{2}(1000)(20^2) = 500 \times 400 = 200,000\text{ Joules (200 kJ)}$$
Teacher Strategy Tip:
Remind students that acceleration due to gravity $g$ on Earth is $10\text{ m/s}^2$ or $9.8\text{ m/s}^2$ as specified on Page 2 of the ECZ Physics paper!
SI Units Checklist:
Always verify units before calculating: mass must be in kilograms ($\text{kg}$), displacement in meters ($\text{m}$), and velocity in meters per second ($\text{m/s}$). Convert $\text{km/h}$ to $\text{m/s}$ by dividing by $3.6$!