Two objects collide. Object A weighs 10 kg moving at 5 m/s. Object B weighs 5 kg at rest. After the collision they stick together. What is their combined velocity? (Conservation of momentum.)

Conservation of momentum: in any collision (elastic or inelastic), total momentum before = total momentum after, IF no external forces act on the system. Momentum p = mass × velocity. Before collision: p_A = 10 × 5 = 50 kg·m/s; p_B = 5 × 0 = 0; total = 50 kg·m/s. After collision (objects stick = perfectly inelastic): combined mass = 10 + 5 = 15 kg; total momentum still 50 kg·m/s; velocity = momentum / mass = 50/15 = 3.33 m/s. Types of collisions: (1) ELASTIC — kinetic energy AND momentum are conserved; objects bounce off perfectly; idealized — billiard balls approximate this; (2) INELASTIC — momentum conserved, kinetic energy NOT conserved (some becomes heat, sound, deformation); most real collisions; (3) PERFECTLY INELASTIC — objects stick together after collision; momentum conserved, max kinetic energy loss. Newton's third law: every action has an equal and opposite reaction. In a collision, the forces on each object are equal and opposite; force × time on each object causes equal and opposite changes in momentum (impulse-momentum theorem: F·t = Δp). Real-world applications: car safety (airbags, crumple zones extend collision time, reducing peak force); recoil (firearm pushes shooter back; rocket pushes gas back, gas pushes rocket forward); jet propulsion; sports physics (collisions between balls, players). ASVAB MC may include simple momentum conservation problems but more often tests conceptual understanding.