• Quick retrieval from earlier learning (Momentum (p = m v)). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. What is the momentum of a 5 kg object moving at 2 m/s, in kg m/s? → 10 kgm/sPrompt: momentum = mass × velocity
2. An object of mass 1500 kg has a momentum of 18000 kg m/s. What is its velocity, in m/s? → 12 m/sPrompt: Rearrange p = m v.
3. A 0.15 kg ball moving at 20 m/s and a 60 kg runner moving at 0.05 m/s — which has more momentum? (neither has any / the runner / the ball / they have the same momentum) → they have the same momentumPrompt: Work out m × v for each.

• Drop a sheet of paper and a scrunched-up sheet together and ask why one falls faster.
• Share the objective: Conservation of momentum in collisions and explosions. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A 2 kg trolley moving at 4 m/s hits a stationary 4 kg trolley. They stick together. What is their velocity just after the collision, in m/s? (Give 2 decimal places.)
• Step 1: 2 × 4 = 8
• Step 2: v = 8 ÷ 6 = 1.333
• Step 3: So the answer is: 1.33 m/s
• Answer: 1.33 m/s
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. A 2 kg trolley moving at 10 m/s hits a stationary 2 kg trolley. They stick together. What is their velocity just after the collision, in m/s? (Give 2 decimal places.) → 5 m/sPrompt: Total momentum before = total momentum after.
2. A 5 kg toy cannon at rest fires a 0.05 kg ball forwards at 400 m/s. What is the recoil speed of the cannon, in m/s? → 4 m/sPrompt: The total momentum before firing is zero.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A 1000 kg car moving at 4 m/s hits a stationary 1500 kg car. They lock together. What is their velocity just after the collision, in m/s? (Give 2 decimal places.) → 1.6 m/sPrompt: Total momentum before = total momentum after.
2. In which situation is momentum conserved? (in a closed system with no external forces / only in elastic collisions / never / only when objects are stationary) → in a closed system with no external forcesPrompt: External forces can add or remove momentum.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.