Which equation represents Newton's second law?

• A. E=mc^2
• B. V=IR
• C. P=VI
• D. F=ma

Answer: (D)

The motion of an object changes in response to the net external force acting on it, and that change in motion is described by F = m a. This equation says that the acceleration a of a mass m is proportional to the net force F applied and points in the same direction as that force. In other words, doubling the net force while keeping mass the same doubles the acceleration, and increasing the mass for the same force halves the acceleration. The mass provides inertia, resisting changes in motion, so a larger mass requires a larger net force to produce the same acceleration. The vector nature matters: force and acceleration point in the same direction, and when multiple forces act, you add them to get the net force before applying the equation.

Other common formulas, like E = mc^2, describe energy-mass equivalence rather than motion under forces, and Ohm’s law or the related P = VI describe electrical behavior, not the mechanics of objects moving under forces.