# Another Physics problem

• Oct 27th 2012, 11:06 AM
Louisana1
Another Physics problem
A 1200 kg car traveling north at 10 m/s is rear-ended by a 2000 kg truck traveling at 31 m/s. What is the total momentum before and after the collision?

before collision_______
after collision___________

Who said physics was easy online. (Headbang)
• Oct 27th 2012, 11:53 AM
johnsomeone
Re: Another Physics problem
Prior to the collision, can you find the magnitude of the momentum of the car?
Of the truck?
Now what about their directions, hence their momentum? (Remember that momentum is a vector!)
So what was the total momentum (= momentum car plus momentum truck) prior to the collision? (Again, remember that momentum is a vector!)
If you know the total momentum prior to the collision, what can you say about it after the collision?
• Oct 27th 2012, 02:51 PM
Louisana1
Re: Another Physics problem
put in number so I can read thx I'm super lost
• Oct 27th 2012, 03:39 PM
topsquark
Re: Another Physics problem
Quote:

Originally Posted by Louisana1
put in number so I can read thx I'm super lost

No numbers are needed. The net external force on the car and the truck system is 0 N. What can we say about the total momentum in this case? (Hint: The concept here is one that you will almost always use for problems dealing with total momentum.)

-Dan
• Oct 28th 2012, 08:25 AM
johnsomeone
Re: Another Physics problem
I'll do a piece to get you started.
The magnitude of the momentum of the truck is mass times velocity = (2000 kg)(31 m/s) = 62,000 kg m / s.
The truck's direction of motion?
Since the truck rear-ended the car, the truck was moving in the same direction as the car. Since the car was travelling north, so was the truck.
Therefore the truck's momentum (a vector!) prior to the collision was 62,000 kg m / s due north.