Colliding masses

1. Jan 3, 2008

Joza

2 vehicles, one traveling north, the other east, collide and stick together. Their combined mass then slides at a given speed v_3, at a given angle to the east of north.

I also have the masses of the vehicles. I need to find their velocities before crashing. Ignore friction.

So my idea is that the total kinetic energy after the collision is equal to the sum of the kinetic energies of the vehicles before the collision.

I come up with a general equation of the form:

x^2 + y^2 = z, where z is a known number. This of course can't be solved because of the 2 unknowns. So the information I need must lie with the angle given. But I can't figure it out.

Any pointers in the right direction?

2. Jan 3, 2008

Staff: Mentor

Since the vehicles stick together, the collision is perfectly inelastic: KE is not conserved. What is?

3. Jan 3, 2008

momentum?

4. Jan 3, 2008

Staff: Mentor

Absolutely. And since momentum is a vector, set up two equations: one for the x-components (east - west) and another for the y-components (north - south).

5. Jan 3, 2008

Joza

I haven't read that chapter yet. I'm a bit behind.

I presumed it was energy, that's where I'm up to so far...I'll be there tomoro. Cheers!