Work against gravity is proportional to mass times height on the same planet

Steps:

• Determine gravitational acceleration g from initial case: g = work / (mass × height) = 30 J / (1 kg × 10 m) = 3 m/s².
• Apply formula for new case: work = mass × g × height = 4 kg × 3 m/s² × 5 m.
• Calculate: 4 × 3 = 12, then 12 × 5 = 60 J.

Why B is correct:

• 60 J equals mgh with g constant, as work against gravity follows W = mgh per Newton's law of universal gravitation adapted to surface g.

Why the others are wrong:

• A: Ignores mass quadrupling, underestimates by halving original work.
• C: Overestimates by using original height instead of halved height.
• D: Misapplies by assuming Earth's g (≈10 m/s²), yielding 4 × 10 × 5 = 200 J.

Final answer: B