Work, Energy & Momentum — Extension · Physics & Environmental Science, Grade 12
Account for work, power, stored energy, collisions, and force-time evidence.
Impulse and Energy Accounting
Investigate
Can two force pulses give the same momentum change?
Use two dedicated sessions: first define the model, boundary, variables and comparison, then collect suitable records or analyze the complete supplied-data route; second complete calculations/graphs, compare alternatives, revise and prepare the report. Extend collection time where needed. Supplied-data work does not certify supervised laboratory minutes or mandated investigations.
Materials
- Notebook, graph paper, and calculator
- The supplied data table is sufficient for analysis
- Optional household setup described in the method; an adult checks safety
Before you begin
Use only the listed household materials or analyze the supplied data. An adult should review setup. No flames, strong acids/alkalis, unknown chemicals, household mains, radiation sources, or high-speed projectiles are needed. Keep food-study materials separate from eating and wash hands afterward.
Plan a fair test
Compare ideal constant force pulses with equal area. The 1 kg object starts at rest and has negligible other impulse.
Method
- Write a prediction and the mechanism that supports it.
- Draw the setup or boundary; label axes, quantities, and units.
- Draw 20 N lasting 0.10 s and 10 N lasting 0.20 s on common axes.
- Calculate each signed area and resulting velocity.
- Calculate final kinetic energy and distinguish average from peak force.
- Record independent repetitions where possible, raw values, and instrument resolution.
- Write a claim citing numerical evidence, a limitation, and a follow-up test.
Example data — for analysis when materials are unavailable
Illustrative teaching data, not measurements from a real district laboratory. Analyze these when materials are unavailable and identify them as provided data. Do not claim to have performed a measurement you did not make.
| Pulse | Averageforce (N) | Duration (s) | Impulse (N·s) |
|---|---|---|---|
| A | 20 | 0.1 | 2 |
| B | 10 | 0.2 | 2 |
Analyze and explain
- Find final velocity for each pulse.
- Find final kinetic energy.
- Why does lower average force not imply less impulse here?
- Link the pattern to a labeled particle, structure, energy or amount model from the chapter.
- Distinguish supplied illustrative records from measurements actually collected.
- Identify uncertainty and propose a comparison that would test an alternative explanation.
What a strong explanation includes
- A stated prediction, conditions, and controlled variables or explicit model boundary.
- A labeled table/graph with units, calculations, and attention to repeated values or uncertainty.
- A claim citing numerical evidence and a scientifically accurate mechanism.
- A limitation, alternative explanation, and useful follow-up test.
- Preserve initial reasoning and an evidence-supported revision.
- Check units, object/material identity, system boundary and physical assumptions.
Parent / teacher guide: discuss after the investigation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.
Extend the chapter investigation by evaluating its evidence and proposing a better test.
Problem 1
Answer and explanation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 2
Answer and explanation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 3
Answer and explanation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 4
Answer and explanation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 5
Answer and explanation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 6
Answer and explanation
Both pulses give 2 N·s impulse, so the 1 kg object reaches 2 m/s and 2 J kinetic energy. Twice the duration compensates for half the force. Real peak forces and motion need more detailed time profiles. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.