# Crash Crash Question

1. Jun 24, 2009

### JordaanDMC-12

Hello everyone, my name is Jordan and I love Physics... Well my main question is, when two cars get into an accident, lets say one vehicle is traveling at a velocity of 40 miles per hour, the other vehicle at the same 40 miles per hour. When they get into a head on collision, you add the two velocities together right? So in fact the vehicles were subjected to a crash at the force of 80 mph?

Is this correct?

2. Jun 24, 2009

### mgb_phys

Basically yes.
In detail in a real crash it might make a difference - so accident investigators could probably tell if both cars where moving or not.

3. Jun 24, 2009

### Danger

Quite right. One of the major components of the problem will be the relative weights and structural integrities of the vehicles. At the speeds that you mentioned, a Hummer would come out fairly unscathed in a crash with a Smart car. Might need a new bumper, and a repacked airbag, but the frame would probably be fine.

4. Jun 24, 2009

### PatPwnt

What is the definition of a crash? Two cars that are the same mass and going equal opposite velocities that collide head on will be similar to one of the cars colliding with an immovable wall. Or one of the cars colliding at twice the velocity with the another car at rest.

5. Jun 24, 2009

### Naty1

The above answers may not get to the more accurate underlying principle that it's relative , momentum that provides a better insight....mv =Mv where M is much bigger than m, "M" is the Hummer..

In other words, if the two vehicles are identical, the velocities tell just about the whole story; but if one vehicle is twice as heavy as the other, it's momentum will be twice the other vehicle at any identical velocity......at the crash, the twice a heavy Hummer will still be moving in its original direction while the smaller vehicle will be forced backwards.....

6. Jun 24, 2009

### JordaanDMC-12

So this is what I am basing this on: