Elastic Collisions
- When two objects collide, they may spring apart retaining all of their kinetic energy. This is a perfect elastic collision
- An elastic collision is one where kinetic energy is conserved
Equation for kinetic energy
- Since kinetic energy depends on the speed of an object, in a perfectly elastic collision (head-on approach) the relative speed of approach = the relative speed of separation
Worked example
Two similar spheres, each of mass m and velocity v are travelling towards each other. The spheres have a head-on collision. What is the total kinetic energy after the impact?
Examiner Tip
Despite velocity being a vector, kinetic energy is a scalar quantity and therefore will never include a minus sign. This is because in the kinetic energy formula, mass is scalar and the v2 will always give a positive value whether its a negative or positive velocity