D.4-Choosing formulae without losing physical reasoning

1. Name the system/process. 2. List known and target quantities. 3. State assumptions/conditions. 4. Select a relation containing the target and usable knowns. 5. Rearrange symbolically. 6. convert SI and calculate. 7. check unit, sign, scale and interpretation.

When several models could give energy, identify the transfer mechanism: ΔEₖ=mv²/2 for speed change, ΔEₚ=mgΔh near Earth, W=Fs cosθ for a force through displacement, E=Pt for steady power. Compare like quantities only after calculating each under its conditions.

A formula given in the question may be unfamiliar. Treat it as a model: define each symbol from the stem, inspect powers/roots, rearrange for the requested quantity, and derive the unit from the expression.

Show the selected equation and numerical substitution so method marks remain visible. Keep more figures than the final answer and carry previous answers at full precision where possible.

Finish in physics language: direction from sign, larger/smaller from a ratio, valid/invalid from conditions, or agreement/disagreement within precision. A bare number is not an explanation.

Matching symbol letters is not model selection: the same letter can mean different quantities, and the right variables in a relation do not guarantee that its assumptions hold.