- Practice · 5 marks
Needs, goals, constraints and criteria
Short answer
Need is what the user requires; goal is a measurable target; constraint is a must-meet limit; compromise is a trade-off. A problem statement is short, solution-neutral, and measurable, stating function, constraints, and targets. For a hand pump, example: raise ≥10 L/min from 10 m, force ≤150 N, cost <Rs 5000. Evaluation criteria like discharge, cost, reliability are weighted.
Differentiate between needs, goals, constraints and compromises in a design problem. Explain how a good problem statement is written and the criteria for evaluation are set, using the design of a hand-operated water pump for a village household as the example.
Differentiation
| Term | Meaning | Example (hand pump) |
|---|---|---|
| Need | What the user requires; the reason for the design | Safe drinking water from a well for a household |
| Goal | A desirable target that should be achieved as far as possible; it may be measured | Low cost, light weight, easy to repair locally |
| Constraint | A limit that must not be violated; a pass/fail requirement | Lift of 10 m, flow at least 10 litre/min, cost below Rs 5000, made from locally available materials |
| Compromise | A trade-off between conflicting goals or constraints | Thicker pipe gives long life but increases cost, so a medium thickness is chosen |
Conditions are the working circumstances (outdoor use, dusty and wet, operated by a child or an adult). Criteria for evaluation are the measures used to compare alternatives, taken from the goals and constraints.
Writing the problem statement
A good problem statement is short, specific, solution-neutral, and measurable. It says what is to be achieved, not how. It includes the user, the function, the main constraints and the performance targets.
Example: "Design a hand-operated pump to raise at least 10 litre/min of water from a depth of 10 m for a family of six. Operation force should not exceed 150 N, the cost should be below Rs 5000, and it should be maintained with common tools."
Criteria for evaluation for the pump
- Discharge and ease of operation (force, stroke).
- Initial cost and cost of maintenance.
- Reliability and life.
- Use of local materials and skills.
- Safety and hygiene (no contamination of water).
Each criterion is given a weight and each concept is scored (decision matrix) so that the best design is selected objectively.
✓ Answer checked by Claude Opus 5.5 (high effort)
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