Power equals work done divided by time

Steps:

• Work done to raise lift: W = m g h, with g ≈ 10 m/s².
• W = 1500 kg × 10 m/s² × 20 m = 300,000 J.
• Power P = 20 kW = 20,000 W.
• Time t = W / P = 300,000 J / 20,000 W = 15 s.

Why B is correct:

• 15 s matches t = m g h / P from the work-energy principle at constant speed.

Why the others are wrong:

• A: 5 s implies unrealistically high power of 60 kW.
• C: 30 s assumes g = 5 m/s², not standard.
• D: 60 s implies only 10 kW power output.

Final answer: B