Collisions with increase in total kinetic energy

What types of interactions result in an increase in total kinetic energy?

Separation of two bodies with a compressed spring, Recoil, Explosion.

What principle is always conserved when total kinetic energy increases in a system?

The total energy of the system (initial total energy = final total energy).

What happens when Two Bodies with a Compressed Spring separate?

Elastic potential energy of the spring converts to kinetic energy of the bodies, increasing system KE.

What is the total momentum of a system of two bodies at rest with a compressed spring before release?

Zero.

What is the total momentum of a system of two bodies after release from a compressed spring?

Zero, as total momentum is conserved (bodies move in opposite directions with same magnitude of momentum increase).

What is Recoil?

The backward motion of a gun when it fires a cannon ball in the forward direction.

What energy conversion occurs during Recoil?

Potential energy in the gun converts to kinetic energy of the cannon ball and the gun, increasing system KE.

What is the total momentum of a gun and cannon ball system before firing?

Zero (initially at rest).

What is the total momentum of a gun and cannon ball system immediately after firing?

Zero, as total momentum is conserved (momentum of gun increases opposite to cannon ball, with same magnitude).

What is an Explosion?

Large forces act on fragments of a stationary body, ejecting them at high speeds in different directions.

What energy conversion occurs during an Explosion?

Mainly kinetic energy of fragments; total KE of the system increases after explosion. Also sound and thermal energy produced.

What is the total momentum of a system during an explosion?

Total momentum is conserved, equal to zero (assuming body was at rest before explosion), because explosive forces are internal.

Why is gravitational force's effect negligible during explosions?

Explosive force is very large and duration of explosion is very small, making its effect on fragment momenta more significant than gravity. Conservation of momentum applies immediately before and after explosion.