Power equals total opposing force times speed for constant velocity

Steps:

• Component of weight parallel to incline: 1800 N × sin 30° = 900 N down the slope.
• Total opposing force: gravitational component + resistive force = 900 N + 240 N = 1140 N.
• Useful output power P = opposing force × speed, so speed v = P / opposing force = 3600 W / 1140 N = 11 m/s (rounded appropriately for options).
• Verify units: watts = newtons × meters/second, consistent.

Why B is correct:

• Follows the formula P = (mg sin θ + R) v, where solving for v gives 11 m/s directly from given values.

Why the others are wrong:

• A ignores part of gravitational component, underestimating speed.
• C neglects gravitational component entirely, overestimating speed for flat road.
• D uses only partial resistance, yielding unrealistically high speed.

Final answer: B