# Conservation of momentum of two cars

1. Jul 23, 2007

### Stipe

For my physics assignment i have a question on conservation of momentum that i am completely unsure of and have heard mixed answers to from teachers and fellow students. Here is the question and can ai have nice detailed answers please. Thanks in advance.

Section A - conservation of momentum

In a real life collision between your two chosen cars ( Honda civic and Toyota Camry (sp?) ) on a bitumen road on a dry day, is it reasonable to assume that the total energy and momentum of the cards is conserved? Explain your answer.

2. Jul 23, 2007

### xez

In the title you address this as an issue of
"Conservation of momentum"
whereas in the bold face at the bottom you say:
"is it reasonable to assume that the total energy and momentum of the cards is conserved?"

...conserving momentum only is very different than
conserving (energy and momentum in combination).

Obviously momentum can convert to other kinds of
energy than kinetic energy e.g. thermal, stress, ....

Clearly you don't see elastic collisions between
cars other than bumper cars... and as for inelastic collisions,
well, usually on the highway I see more CRUNCH than
BOING/BOUNCE....

And how does an air-bag work again?....

So think of all the kinds of resultant MOMENTUM, but
then think of all the energy dissipated in other ways,
the conversion of kinetic energy to other kinds, etc....

What do you think?