Boyle's Law for constant temperature

Steps:

• Initial length L1 = 20 cm, so initial volume V1 ∝ 20; pressure P1 = p.
• Piston moves out, new length L2 = 20 + 40 = 60 cm, so V2 ∝ 60.
• At constant temperature, Boyle's Law: P1 V1 = P2 V2.
• Solve: p × 20 = P2 × 60 → P2 = (20p)/60 = p/3.

Why B is correct:

• Boyle's Law states that pressure is inversely proportional to volume at constant temperature, so tripling volume halves pressure twice, yielding p/3.

Why the others are wrong:

• A: Assumes doubling volume halves pressure, but volume triples.
• C: Reverses the inverse relationship, as if volume decreased.
• D: Ignores inverse proportionality, treating pressure as directly proportional.

Final answer: B