A car travelling at a velocity v is struck from behind by a car of the same mass travelling with velocity 2v.?

Cont.-> If the cars lock together,wat wil be their common velocity?..About conservation of energy n collisions..D collision can b elastic collisions o inelastic collisions..Thnkz u

initial momentum = final momentum
(mv) + (m*2v) = (m + m) * (V)
mv + 2mv = 2m(V)
3mv = 2m(V)
1.5v = V

Therefore, common velocity is 1.5v

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to find out whether this is elastic or inelastic collision, find their total kinetic energy for the initial and final momentum:

initial momentum = final momentum
[½mv²] + [½m(2v)²] = ½(2m)V²
½mv²+ 2mv² = ½(2m)(1.5v)²
2½(mv²) â‰* 2¼mv²

since the kinetic energy of the initial and final momentum is different, the collision is INELASTIC!!

conservation of momentum

initial momentum = mv + 2mv = 3mv

final momentum = initial = 3mv = V(2m)
3mv = 2mV
V = (3/2)v

I don't understand the second part of your question, the spelling is too bad. Something about conservation of energy. This is NOT conserved in a collusion, in the sense that ½mV² is not conserved. It is conserved if you consider that some of the energy is turned into heat (and sound).

Yes, collisions can be elastic or not.

Other answer is correct IF in the second section, you change the word "momentum" to "kinetic energy"

mv + 2mv = 2ms
3mv = 2ms
1.5v or 1.5 times the original velocity