# Conservation of momentum of a colliding car

## Homework Statement

A 1200 kg car moving eastward at 8 m/s approaches an intersection where it unfortunately collides with an 1800 kg car going southward at 6 m/s. If they stick together, how fast do they move after the collision? The answer is 4.82 m/s

## Homework Equations

a^2+b^2=c^2, p=mv, p before + p before = p after + p after

V=mv+mv/m+m

## The Attempt at a Solution

LowlyPion
Homework Helper
I think you will want to resolve the momentum into x,y momentum equations and determine the x,y velocity components, before using the Pythagorean.

I think you will want to resolve the momentum into x,y momentum equations and determine the x,y velocity components, before using the Pythagorean.

how do i determine the velocity components?? i can get the momentum components easily by multiplying the velocity and mass...right?

LowlyPion
Homework Helper
how do i determine the velocity components?? i can get the momentum components easily by multiplying the velocity and mass...right?

The car going East is can be be expressed as

M1V1 = M1*|V1| x + 0 y = 1200*8 x = 9600 x

And the one going south ...

M2V2 = 0 x + M2*|V2| y = 1800*(-6) y = - 10800 y

Now you have an inelastic collision, so in the X direction

9600 = V'*(1200 + 1800) x = 9600/3000 x

and so on until you have the 2 components of the final V'.