How Fast Was the Truck Moving Before the Collision?

[twistedcolors]

Homework Statement

Two vehicles stick together as a result of the collison. If the 900 kg car was initially at 12 m/s east, then with what speed was the 2200 kg truck traveling north if they move off together in a direction equally north and east.

Homework Equations

MV = P
Pi = Pf
(M1)vi + (M2)vi = Mvf

The Attempt at a Solution

I worked out the equation, but I got lost after that.
(900)(12) + (2220)(vi) = (900+2200)(vf)
10800 + 2220vi = 3100vf

How would I find vi from that equation?

 

[tiny-tim]

welcome to pf!

hi twistedcolors! welcome to pf!

(M1)vi + (M2)vi = Mvf
…
(900)(12) + (2220)(vi) = (900+2200)(vf)

nooo …

https://www.physicsforums.com/library.php?do=view_item&itemid=53" is a vector, and the conservation of momentum is a vector equation …

you need to take components in a particular direction

try again! ​