AS Physics Linear Momentum Question

AI Thread Summary
The discussion revolves around calculating the total momentum of a lorry and a car before their collision. The lorry, with a mass of 20,000 kg traveling at 20.0 m/s, has a momentum of 400,000 Ns, while the car, weighing 900 kg and moving at 30 m/s, has a momentum of 27,000 Ns in the opposite direction. The total momentum is found by subtracting the car's momentum from the lorry's, resulting in 373,000 Ns. However, there is confusion as the textbook states the answer is 427,000 Ns, leading to concerns about a possible error in the textbook. The discussion concludes with the user planning to address the discrepancy with their teacher.
seiei
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Homework Statement


A lorry of mass 20,000kg is traveling at 20.0m/s towards a car of mass 900kg traveling at 30m/s towards the lorry. What is the magnitude of the total momentum?


Homework Equations


m1u1+m2u2=p1
Not sure about any others :\

The Attempt at a Solution


The lorry has a momentum of 400,000Ns in the positive direction and the car has a momentum of 27000Ns in the negative direction but this is before impact. Not sure how to go about this, any help would be appreciated.
 
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welcome to pf!

hi seiei! welcome to pf! :smile:

(try using the X2 icon just above the Reply box :wink:)
seiei said:
The lorry has a momentum of 400,000Ns in the positive direction and the car has a momentum of 27000Ns in the negative direction but this is before impact.

That's fine :smile: … what's worrying you about that? :confused:

The total https://www.physicsforums.com/library.php?do=view_item&itemid=53" is just the sum (400000 - 27000), and it's the same before as after the collision anyway …

momentum (and https://www.physicsforums.com/library.php?do=view_item&itemid=313")
 
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tiny-tim said:
hi seiei! welcome to pf! :smile:

(try using the X2 icon just above the Reply box :wink:)


That's fine :smile: … what's worrying you about that? :confused:

The total https://www.physicsforums.com/library.php?do=view_item&itemid=53" is just the sum (400000 - 27000), and it's the same before as after the collision anyway …

momentum (and https://www.physicsforums.com/library.php?do=view_item&itemid=313")


Oh right, I'll remember that for next time :D! Yeah I thought the answer was 373kNs but the textbook answer said 427kNs... I was getting kinda confused. Anyways, it's probably just an error in the answers so I'll tell my teacher about that, thanks for the help!
 
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