# Homework Help: Inelastic collision question

1. Oct 4, 2004

### phy

Hi everyone. I need some help with the following question.

In a traffic accident, a car of mass 2000kg travelling south collided in the middle of an intersection with a truck of mass 7000kg travelling west. The vehicles locked and skidded off the road long a line pointing southwest. A witness claimed that the truck had entered the intersection at 80km/hour.
a) Do you believe the witness? Why/why not?
b) Find the velocities of the vehicles before and after the collisions in the centre of mass frame.
c) How much kinetic energy is lost in the collision?

My problem is that I think there are too many values that are not given. I tried using the equation m1v1+m2v2 = (m1+m2)v' but then I didn't know what values to use for v1 and v'. Does anybody have any thoughts on this?

2. Oct 4, 2004

### e(ho0n3

Yes, it would seem the problem is unsolvable unless you know: the velocity of the car, the velocity of the combined car/truck after collision, or another equation relating these quantities.