Work equals force times parallel displacement

Steps:

• Force F acts parallel to the slope.
• Block displaces distance l along the slope.
• Work by F uses dot product: F · displacement = F l cos(0°) = F l.
• No other components affect F's work directly.

Why B is correct:

• Work-energy theorem defines work as force magnitude times displacement magnitude when parallel.

Why the others are wrong:

• A: h is vertical height, not displacement along F's direction.
• C: W is gravitational force, d is undefined and unrelated to F.
• D: Substitutes weight W for applied force F.

Final answer: B