Car-Truck Collision: Initial Common Velocity

[Mr.somebody]

Homework Statement

A car with a mass of 1400 kg is westbound at 50 km/h. It collides at an intersection with a northbound truck having a mass of 2000 kg and traveling at 40 km/h. What is the initial common velocity of the car and truck immediately after the collision if they have an inelastic collision? For this question, a diagram is drawn for you. The mass' stick after colliding[/B]

Homework Equations

p=mv

The Attempt at a Solution

So i tried 2 different methods
m1v1+m2v2=mv* and the other method i used was that i drew a triangle (made vectors) found the hypotenuse (momentum combined) and from there i divided by the mass to get the velocity.
When i did this i got 2 different answers I am really confused which one is correct please help :)

 

[Qwertywerty]

Momentum is a vector and so you need to pay attention to the directions .

The best and easiest way to solve this question would be to conserve momentum along north-south direction , and then along east west , and then simply find the net magnitude of velocity .

I cannot understand what exactly you have written , but from what I can tell , method 2 seems to be correct .

 

[Alex.malh]

Both methods are correct. The second method is just a graphical representation of the first.
But as Qwertywerty said: you can't just add vectors.

 

[Mr.somebody]

Oh, okay thank you soo much guys I get it now :)