Momentum is defined as the product of which quantities?

• A. Mass and velocity
• B. Distance and time
• C. Mass and acceleration
• D. Force and time

Answer: (A)

Momentum describes how much motion an object has, defined as the product of its mass and its velocity. In symbols, p = m v. Since velocity includes direction, momentum is a vector that points in the same direction as motion. Units come out as kilogram meters per second (kg·m/s). This definition shows how changing either mass or velocity changes the amount of motion an object possesses—for example, a 2 kg object moving at 3 m/s has momentum 6 kg·m/s. The other ideas correspond to different concepts: distance and time give speed, mass and acceleration relate to force via F = m a, and force multiplied by time gives impulse (the change in momentum), not momentum itself.