# Ineleastic perpendicular collision question

1. Apr 23, 2017

### MomentumIsHard

1. The problem statement, all variables and given/known data
Car 1: 2200kg
Initial direction: South
Car 2: 1800kg
Initial direction: East
Cars lock together and slide 11.25M (S 22.25 E)
At an acceleration that is 9.81 m (back) (it's a coincidence that this is gravity.)
2. Relevant equations
Who's fault was the collision if the speed limit was 50km/h?

I can't find momentum without a velocity so I'm very lost

3. The attempt at a solution

2. Apr 23, 2017

### haruspex

Just invent variables to represent the three unknown velocities, the two before and the one after collision.
Momentum gives you two equations, stopping distance gives you a third.

3. Apr 23, 2017

### MomentumIsHard

Which equations are those? We only got one equation for in elastic in class, what about the distance one too? What you said makes sense but I can't find 3 equations

4. Apr 23, 2017

### Staff: Mentor

Hi MomentumIsHard,

You need to make some attempt before help can be given. What details about the motion after the collision do you know?

5. Apr 23, 2017

### MomentumIsHard

All the question states is that it moves 11.25 M [Back] (even though other directions were given in terms of east and south) at an acceleration of 9.81 m/s. The problem is I don't know where to start so I can't really make an attempt. Once I get one momentum I could pretty easily figure this out but I can't quite figure that out with no velocities given

6. Apr 23, 2017

### haruspex

Conservation of momentum (one for each of two dimensions) and the SUVAT equation relating speeds, distance and (constant) acceleration.

7. Apr 23, 2017

### Staff: Mentor

No idea what "[Back]" is supposed to mean, but it doesn't matter if you're given the rest of the motion details. You have a distance, an acceleration, and a final speed. What can you deduce from that?

8. Apr 23, 2017

### haruspex

I think it means the direction of the given acceleration is opposite to the motion.

9. Apr 23, 2017

### Staff: Mentor

That's quite likely. Of course deceleration is also implied by the fact that the combined mass travels a limited distance.