What is the equation for finding the velocities of colliding masses?

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Homework Help Overview

The discussion revolves around a collision problem involving two vehicles that collide and stick together, moving at a combined speed and angle after the collision. The original poster seeks to determine the velocities of the vehicles prior to the collision, given their masses and the resulting motion.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster proposes using kinetic energy conservation to relate the pre-collision velocities to the post-collision speed and angle but recognizes the challenge due to multiple unknowns. Participants suggest focusing on momentum conservation instead, particularly emphasizing the need to set up equations for both x and y components of momentum.

Discussion Status

Participants are exploring the principles of momentum conservation in the context of a perfectly inelastic collision. Some guidance has been offered regarding the setup of momentum equations, but the original poster has indicated a lack of familiarity with the relevant concepts, suggesting a need for further clarification and study.

Contextual Notes

The original poster mentions being behind in their studies, indicating that they have not yet covered the chapter on momentum, which may affect their understanding of the discussion.

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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?
 
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Since the vehicles stick together, the collision is perfectly inelastic: KE is not conserved. What is?
 
momentum?
 
Joza said:
momentum?
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).
 
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!
 

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