Understand the core concepts covered in this lesson.
Apply your knowledge to solve problems and explain phenomena.
Evaluate and analyse scientific information and data.
This final lesson is where the module stops feeling like separate chapters. A real dynamics problem often begins with forces, shifts into motion, turns into energy, and ends with impulse or momentum. Your job now is to recognise the chain and choose the right law at the right moment.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
A trolley is pushed, speeds up, collides with another trolley, and then both slide to rest.
Before reading: which ideas from this module would you expect to use, and in what order? Write the chain you would try first.
Wrong: An object moving at constant velocity has no forces acting on it.
Right: An object at constant velocity has BALANCED forces (net force = 0), not necessarily no forces.
📚 Core Content
Always draw free-body diagrams before applying Newton's laws. Identifying all forces acting on an object is the first step to solving dynamics problems.
5 random questions from a replayable lesson bank — feedback shown immediately
1. Explain why momentum conservation is usually the preferred model during a collision, while work-energy is often the preferred model before or after the collision. (3 marks)
1 mark collision explanation; 1 mark before/after explanation; 1 mark links to timescale or stage logic
2. A 1.5 kg cart moving at 6.0 m/s collides with a stationary 0.5 kg cart and they stick together. Find the speed immediately after the collision and the kinetic energy lost. (3 marks)
1 mark momentum setup; 1 mark post-collision speed; 1 mark KE loss
3. A student says, “If I know the speed at every point, I don't need to think about forces, energy and momentum separately.” Evaluate this claim using one example from this module. (3 marks)
1 mark claim evaluation; 1 mark example; 1 mark explanation of why different models still matter
Answers
SA1: Momentum conservation is preferred during a collision because the interaction happens over a very short time and the total momentum of a closed system remains constant. Before or after the collision, work-energy is often preferred because forces act through distance over a longer stage, making it easier to connect force, distance and kinetic energy changes.
SA2: Momentum before = $(1.5)(6.0) + (0.5)(0) = 9.0\text{ N s}$. After collision the combined mass is $2.0\text{ kg}$, so $2.0v_f = 9.0$, giving $v_f = 4.5\text{ m/s}$. Initial kinetic energy = $\tfrac12(1.5)(6.0)^2 = 27.0\text{ J}$. Final kinetic energy = $\tfrac12(2.0)(4.5)^2 = 20.25\text{ J}$. Kinetic energy lost = $27.0 - 20.25 = 6.75\text{ J}$.
SA3: The claim is too simple. Knowing speeds is useful, but it does not explain why those speeds change or which conservation law should be used in each stage. For example, in a trolley collision followed by a skid, momentum conservation is needed during the collision to find the new shared speed, while work-energy is then needed to connect friction to the stopping distance. Different models reveal different causes and constraints.
The best synthesis answers do not start with a random formula. They start by recognising the stages, identifying the dominant idea in each one, and carrying the output of one stage into the next.
Put your knowledge of forces, energy and momentum to the test. Answer correctly to deal damage — get it wrong and the boss hits back. Pool: lessons 1–15.
⚔️ Play Boss Battle →Tick when you have finished all questions and checked your answers.
Look back at what you wrote at the start of this lesson. How has your thinking changed? What new connections can you make?