A 3-kg toy car with a speed of 6 m/s collides head-on with a 2-kg car traveling in the opposite direction with a speed of 4 m/s. If the cars are locked together after the collision with a speed of 2 m/s, how much kinetic energy is lost? (in units of Joules)

Answer 1

Given: M1 = 3kg, V1 = 6m/s.
M2 = 2kg, V2 = -4m/s.
V3 = 2m/s = velocity of M1 and M2 after crash.

KEb = 0.5M1*V1^2+0.5M2*V2^2
KEb = 0.5*3*6^2 + 0.5*2*(-4)^2 = 54+16 = 70 J. = Tot. KE before crash.

KEa = 0.5*3*2^2 + 0.5*2*2^2 = 6+4 = 10 J. = Tot. KE after crash.

KEb-KEa = 70-10 = 60 J. = KE lost.