6 – 3 Collisions

Collisions between 2 or more objects are separated into 2 basic categories elastic: the objects rebound after the collision (bounce off) inelastic: the objects move together as one after the collision (hit & stick)

For elastic collisions: Momentum is conserved Kinetic energy is conserved

Ex: given v1i = 4.2 m/s, v2i = -2.3 m/s, and v1f = -2.3 m/s find v2f. pi = pf m1v1i + m2v2i = m1v1f + m2v2f m2v2f = m1v1i + m2v2i - m1v1f v2f = v1i + v2i - v1f v2f = 4.2 m/s + -2.3 m/s - (-2.3m/s) v2f = 4.2 m/s

For inelastic collisions: characterized by permanent deformation. Momentum is conserved Kinetic energy is NOT conserved

Ex: given v1i = 4.2 m/s and v2i = 0 m/s, find vf. pi = pf m1v1i +m2v2i= (m1+m2)vf vf = m1v1i +m2v2i (m1+m2) vf = m1v1i (m1+m2) vf = v1i /2 vf = 2.1 m/s