Work-energy principle: work equals force times parallel displacement

Steps:

• Recall the definition of work in physics: work done by a force is the product of the force and the displacement component in the force's direction.
• Use the formula W = F · d = F d cosθ, where θ is the angle between force and displacement.
• For work to be F times q, q must be the displacement parallel to F (when θ=0, cosθ=1, q=d).
• Eliminate options involving velocity, as work involves displacement, not speed.

Why A is correct:

• By the work definition, W = F s, where s is displacement in the force's direction, directly matching the formula.

Why the others are wrong:

• B: Perpendicular displacement yields cos90°=0, so work is zero, not F times distance.
• C: Velocity relates to power (P = F v), not work, which requires displacement.
• D: Perpendicular velocity also ties to power components, irrelevant to work calculation.

Final answer: A