Which of these quantities is most closely associated with an object's inertia?

• A. Weight.
• B. Energy.
• C. Power.
• D. Mass.

Answer: (D)

Inertia is the resistance an object has to changes in its motion. The amount of matter it contains—the mass—determines that resistance. So the quantity most closely tied to inertia is mass, because a larger mass means you need a bigger push to achieve the same acceleration (F = m a).

Weight is the gravitational force on an object and can change with gravity, so it doesn’t directly measure resistance to motion. Energy describes how much work an object can do or has done, not how hard it is to change its motion. Power is the rate of doing work, again not about resisting acceleration.