Which formula expresses Newton's second law of motion?

• A. p = mv
• B. F = ma
• C. E = mc^2
• D. F = kx

Answer: (B)

The key idea here is how force causes motion. Newton's second law states that the net force acting on an object produces acceleration, and that acceleration scales with the force and inversely with the object's mass. When the mass is constant, this relationship is written as F = ma, meaning the force directly drives acceleration: doubling the force doubles the acceleration for the same mass, and heavier objects accelerate less under the same force. The other formulas describe different ideas: p = mv is momentum, which shifts as velocity changes; E = mc^2 is energy-mass equivalence from relativity; F = kx is Hooke's law for springs, relating force to displacement, not the general force–motion link.