Power equals force times average velocity

Steps:

• Convert distance: 1 km = 1000 m.
• Calculate velocity: v = distance / time = 1000 m / 150 s = 20/3 m/s ≈ 6.67 m/s.
• Compute power: P = force × velocity = 600 N × (20/3) m/s = 4000 W.
• Convert units: 4000 W = 4 kW.

Why B is correct:

• Power is work per unit time (P = W/t = F × d / t = F × v), yielding 4 kW from the given force, distance, and time.

Why the others are wrong:

• A: 4 W ignores the 1000 m conversion, treating 1 km as 1 m.
• C: 10 kW assumes incorrect time (e.g., 60 s) or velocity.
• D: 90 kW overestimates by using wrong distance or time (e.g., 1 km in ~6.7 s).

Final answer: B