Saturday, January 14, 2017

This car was involved in a car crash.  In all collisions (and explosions) there is Conservation of Momentum.  The total momentum in the system before the crash equals the total momentum in the system after the crash.  The system in this case includes the tractor trailer which crashed into the car and the Earth.  The study of this conservation begins with straight line collisions and explosions.

If m1 is the mass of the first object, then you know what m2 is.
If v1 is the velocity of the first object before the crash, then you can guess what v2 is

Let v1' be the velocity of the first object after the crash.
Let v2' be the velocity of the second object after the crash.

You now have all of the symbols to make the one dimensional momentum conservation equation.

Momentum before = Momentum after becomes

m1v1  +  m2v2     =    m1v1'  +  m2v2'

Here is a twist:  if the two masses stick together, then they have the same velocity v' immediately after the crash (before transferring momentum to the Earth).   In this case

m1v1  +  m2v2     =  (m1 + m2) v'

Try some problems:


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