How Fast Was the Truck Moving Before the Collision?

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The discussion revolves around a physics problem involving a collision between a car and a truck, where both vehicles stick together post-collision. The car weighs 900 kg and travels at 12 m/s east, while the truck's weight is 2200 kg, and its initial speed is unknown. The conservation of momentum equations are applied, but the user struggles with isolating the truck's initial velocity. It is emphasized that momentum conservation must consider vector components for accurate calculations. The conversation encourages revisiting the problem with a focus on vector directions to solve for the truck's speed.
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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?
 
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welcome to pf!

hi twistedcolors! welcome to pf! :smile:
twistedcolors said:
(M1)vi + (M2)vi = Mvf
…
(900)(12) + (2220)(vi) = (900+2200)(vf)

nooo :redface: …

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 :wink:

try again! :smile:​
 
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