Collisions & Explosions in One-Dimension (HL IB Physics)

• In both collisions and explosions, momentum is always conserved
  • However, kinetic energy might not always be

Elastic and inelastic collisions

• Collisions are when two or more moving objects come together and exert a force on one another for a relatively short time
• Explosions are when two or more objects that are initially at rest are propelled apart from one another
• Collisions and explosions are either:
  • Elastic – if the kinetic energy is conserved
  • Inelastic – if the kinetic energy is not conserved

• A perfectly elastic collision is an idealised situation that does not actually occur everyday life
• Perfectly elastic collisions do occur commonly between particles 
  • All collisions occurring on a macroscopic level are inelastic collisions
  • However, exam questions can use the theoretical idea of an elastic collision on a macroscopic level

• A totally inelastic collision is a special case of an inelastic collision where the colliding bodies stick together and move as one body
• In a totally inelastic collision, the maximum amount of kinetic energy is transferred away from the moving bodies and is dissipated to the surroundings

Elastic collisions are where two objects move in opposite directions. Inelastic collisions are where two objects stick together

• An explosion is commonly to do with recoil
  • For example, a gun recoiling after shooting a bullet or an unstable nucleus emitting an alpha particle and a daughter nucleus

• To find out whether a collision is elastic or inelastic, compare the kinetic energy before and after the collision
• The equation for kinetic energy is:

• Where:
  • E_k = kinetic energy (J)
  • m = mass (kg)
  • v = velocity (m s^–1)