stuck at momentum collision question

RMC1989

In a road accident, a car of mass 2000kg, travelling south, collides in the middle of a junction with a truck of 6000kg travelling west. The wreckage of the vehicles locks together and skids off the road along a line pointing exactly southwest. Later a witness tells the police that the truck had entered the intersection at exactly 50mph
1. Is it likely that the witness is correct?
2. If the witness is correct, what fraction of the initial kinetic energy was converted into other forms of energy by the collision?

I know south west is the direction of the resultant velocity when the two vehicles collide and I've worked out that the velocity of the car to be about 38 mph, therefore the resultant velocity is about 250mph. is all this correct? but doing all this doesn't seem to make me any closer to answer question 1 and so I'm stuck please help

Reply 1

manderton

Isn't the resultant the way they are moving?

I've missed a few lessons on this topic, and am working through it slowly on my own, so i could be wrong :biggrin:

think it just asking u for a vector diagram, and finding the angle the resultant is going at is 225 form North.

Reply 2

RMC1989

how does that show the witness is likely to be correct? :confused:

Reply 3

teachercol

If the wreckage moves at 45 then the two vehicles must have the same momentum.

Is this likely?

Reply 4

manderlay in flames

If total momentum before doesn't equal total momentum afterwards (and it won't cos that's what the question is implying) some energy has been converted to other forms, you're meant to work out how much energy this means has been lost (E=mv^2 or something i guess). I'm guessing the amount of energy conversion you'll get will be huge and obviously wrong.