# Inelastic collision

## Homework Statement

A car of mass 950kg travelling at 60km/h in an easterly direction collided perfectly inelastically with another care of mass 1250kg travelling at 55.0km/h in a northerly direction. The design of the smaller care incorporated safety features which ensured that any occupants came to rest relative to the care in a tie of 250m/s. Both vehicles had one occupant of 75.0kg

calculate the velocity of the wreckage immediately after the collision.

Use conservation of momentum to determine the change in momentum of both vehicles

## Homework Equations

m1v1 + m2v2 = m'1v'1 + m'2 v'2
I am not sure if the kinetic energy equation fits here too?
.5 m1 v1 E2 + .5 m2 v2 E2 = .5 m1 v'1E2 + .5 m2v'2E2
r= square root (xE2 +yE2)
p=mv

## The Attempt at a Solution

I converted all the km/h to m/s
I calculated the momentum of each vehicle p=mv (I also included the weight of the driver for each). Using the answers I found the resultant.
I then rearranged the equation to find v and got the right answer in it.

I am now really struggling with the conservation of momentum - these always get me out. I can't seem to use the right equation and am just blank.

Can someone let me know = thank you. :)

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tiny-tim
Homework Helper
Hi Chica1975! I am now really struggling with the conservation of momentum - these always get me out. I can't seem to use the right equation and am just blank.
As I said in the other thread …
You always need two equations to solve a collision question … one is always conservation of momentum, the other is either conservation of energy or some other constraint like "perfeclty inelastic" or " coefficient of restitution = 0.5".
In this case, your second equation (which you did use) is vf1 = vf2

you don't need, and mustn't use, conservation of energy! (But you always need conservation of momentum)