Conservation of Momentum and Collisions

[Charles W]

Homework Statement

A lorry of mass 20,000kg is traveling at 20.0 metres per second. A car of mass 900kg is traveling at 30.0 metres per second towards the lorry.

What is the magnitude of the total momentum?

1. 209 kNs
2. 373 kNs
3. 427 kNs
4. 1045 kNs

2. Homework Equations

Linear Momentum = Mass * Velocity

The Attempt at a Solution

I have tried to find the momentum of each object:

20, 000 * 20 = 40, 000 (for the lorry)
900 * 30 = 27, 000 (for the car)

UPDATE

Can't believe I made such a stupid mistake:

20, 000 * 20 = 400,000

Therefore: 400, 000 - 27, 000 = 373, 000 (Option 2)

 

[Vatsal Sanjay]

Momentum is a vector quantity.

 

[Charles W]

Momentum is a vector quantity.

I am aware of that, but how does it help to solve this problem?

 

[Orodruin]

20, 000 * 20 = 40, 000 (for the lorry)

Check your math (or calculator).

 

[Charles W]

Check your math (or calculator).

That would probably be it - I can't believe I made such a stupid mistake. I'll edit my original question

 

[Vatsal Sanjay]

20, 000 * 20 = 40, 000 (for the lorry)

I think you missed one zero
By the way my apologies, I didn't see you used a minus sign.

 

[Charles W]

I think you missed one zero
By the way my apologies, I didn't see you used a minus sign.

No worries! Thanks for your help :)

 

[Orodruin]

Also note that, as stated, there is not one definite answer. It depends on whether the car is in front of or behind the lorry, since these would imply different directions for "towards the lorry".