# Interview — Proof of work

**Q1. What problem does this mechanism solve?**
How can participants demonstrate computational work when proposing a block? Mine a nonce whose SHA-256 hash has a prefix target; validate claimed work. This is a toy model, not real PoW consensus.

**Q2. What is the naive failure mode?**
A block hash is cheap to calculate; without an acceptance rule anyone can produce many candidates.

**Q3. Is this enough for a secure public blockchain?**
No. This lab isolates one mechanism; production needs cryptographic identities, network rules, adversarial validation, consensus and operational safeguards.

**Q4. What would you test?**
Happy path, malformed input, tampering and disagreement or competing histories where relevant.