Physics Moments problem?

Question

a truck of 2 kg travels at 8m/s towards a stationary truck of mass 6kg. after colliding, the trucks link and move off together

1. what is their velocity after the collision

2. what is the kinetic energy before and after

3. where does the missing energy go

Answer 1

1. m1v1 + m2 v2= (m1+m2) v
2*8 +6*0 =(2+6)v
v= 16/8 =2m/s

2.kE1=1/2 mv^2 =0.5*2*8*8=64
kE2=0.5*6*0*0=0
total kE b4 collision=64J
after collision
kE= 1/2(m1+m2)v^2
=0.5*8*2*2=16 J
3.Change in kE=64-16=48 J
This energy is imparted to the stationary truck to get it moving

Answer 2

By law of conservation of momentum,
2*8=8*x
solving for x we get,
velocity of both trucks is 2 m/s

kinetic energy of first truck is 8 J and second is 0 J
after collision K.E. of both trucks is 2 J and 6 J respectively
so there is no loss in K.E. before and after collision

Answer 3

jst_curious's math is correct, however the reasoning is not. This "energy to get the stationary truck moving" IS its kinetic energy. The difference in energy, however, is dissipated as heat and some is used to break chemical bonds in anything that was broken. Perfectly inelastic collisions such as this dissipate the MOST heat.