Identifying invalid force equations in physics

Steps:

• Recall Newton's second law: force equals mass times acceleration, matching option B.
• Check impulse-momentum theorem: impulse (force times time) equals change in momentum, so force alone does not equal change in momentum.
• Evaluate torque: torque (moment) equals force times perpendicular distance from pivot, allowing rearrangement to solve for force.
• Assess work: work equals force times displacement in the direction of force, but this defines work, not force directly.

Why A is correct:

• Newton's second law and impulse theorem show force equals rate of change of momentum (change in momentum over time), not change in momentum alone.

Why the others are wrong:

• B matches Newton's second law (F = ma).
• C rearranges torque equation (τ = F × d⊥) to F = τ / d⊥, where moment is torque.
• D confuses work equation (W = F × d), but rearranged gives F = W / d for constant force.

Final answer: A