In a head-on, inelastic collision, a 4000kg truck going 10m/s east strikes a 1000kg car going 20 m/s west.?

Question

a) what is the speed and direction of the wreckage?

b) How much Kinetic Energy was lost in the collision?

Answer 1

a) Conservation of momentum. Before collision, total momentum is m1v1 + m2v2; after collision (m1+m2)v (watch the signs of the v's).

b) Kinetic energy before collision = .5(m1v1^2 + m2V2^2). After collision it's .5(m1+m2)v^2; the difference is the energy lost.