Total work is sum of work against friction and gravitational work for lifting

Steps:

• Work against friction: resistive force × distance = 70 N × 6 m = 420 J
• Work to lift: mass × g × height, with g = 9.8 m/s², so 50 kg × 9.8 m/s² × 1.2 m = 588 J
• Total work: 420 J + 588 J = 1008 J, which approximates to 1000 J
• No net kinetic energy change since constant speeds throughout

Why D is correct:

• Matches total work input by agent, per work-energy principle, approximating mgh + friction work to 1000 J with g ≈ 9.8 m/s²

Why the others are wrong:

• A: Only horizontal work against friction, ignores lifting
• B: Equals mg (50 × 9.8), misses height in potential energy
• C: Only lifting work (≈588 J rounded), ignores horizontal friction

Final answer: D