Which of the following best defines a mechanical explosion?

A mechanical explosion is best defined as a build-up of pressure in a container leading to failure. This type of explosion occurs when the internal pressure exceeds the strength of the container, resulting in a sudden and violent release of energy. It can happen in various contexts, such as with pressurized gas cylinders or boilers, where the containment structure is compromised due to excessive pressure.

The other definitions do not align with the characteristics of a mechanical explosion. The sudden release of chemical energy pertains to chemical explosions, which are based on rapid chemical reactions. A rapid reaction involving nuclear materials describes a nuclear explosion, involving nuclear fission or fusion processes, rather than mechanical pressure buildup. An external impact force results in different types of mechanical failure and is not specifically characterized as an explosion in the sense defined. Therefore, the emphasis on pressure and failure in a contained environment accurately captures the essence of a mechanical explosion.