Which object has the greatest inertia?

(1) a 15-kg mass traveling at 5.0 m/s

(2) a 10.-kg mass traveling at 10. m/s

(3) a 10.-kg mass traveling at 5.0 m/s

(4) a 5.0-kg mass traveling at 15 m/s

The correct answer is

(1) a 15-kg mass traveling at 5.0 m/s

In fact, the inertia of an object depends only on its mass. The inertia gives a measure of "how hard is to put an object in motion", or "how hard is to stop an object in motion": the greater the mass, the larger the inertia of the object. In this problem, we have 4 objects, and the object with greatest mass is the first one (15 kg), therefore this is also the object with greatest inertia.