Which collision results when two objects stick together after impact?

• A. Perfectly Inelastic Collision
• B. Elastic Collision
• C. Inelastic Collision
• D. Conservation of Momentum

Answer: (A)

In a perfectly inelastic collision, the two objects collide and stick together, moving as a single combined mass afterward. The key feature is the sticking together, which means some kinetic energy is lost to deformation, heat, or sound, so energy is not conserved in the form of kinetic energy. However, momentum is conserved (assuming no external forces), so the final velocity of the combined mass follows v_final = (m1 v1 + m2 v2) / (m1 + m2).

Elastic collisions, by contrast, involve no permanent deformation and kinetic energy is conserved, with objects typically bouncing apart. An inelastic collision is a broader category where kinetic energy is not conserved, and sticking is just one specific case within that category. Momentum conservation is a principle that applies to many collisions, but it isn’t a type of collision itself.