Homework Help: Conservation of Momentum

1. Sep 4, 2008

ollieman

1. The problem statement, all variables and given/known data

An empty freight wagon of mass 10000kg rolls at 2.0 ms-1 along a level track and collides with a loaded wagon with a mass of 15000kg standing at rest with its breaks realized, If the wagons join together find.

a. their joint speed after the collision.

b. if the collision takes place in 0.1 seconds, what was the acceleration of the moving wagon during the collision

c. what was unbalanced force on the moving wagon during the collision?

d. What was the force on the moving wagon on the stationary wagon?

3. The attempt at a solution

I'm pretty sure the first question uses the law of conservation of momentum

m1u1 + m2u2 = m1v1 + m2v2

But i am just lost with what i need to substitute into this equation :(

2. Sep 4, 2008

LowlyPion

Welcome to PF.

So what kid of collision do you think this is?
Elastic?
Or inelastic?

3. Sep 4, 2008

ollieman

Thanks for replying to my post LowlyPion

i haven't got any idea, it would be the most basic. Since this is my first year studying physics in a physical science course

4. Sep 4, 2008

LowlyPion

In the equation you provided, any idea about what the terms are?

5. Sep 4, 2008

ollieman

$$\sum$$ Pi = $$\sum$$ Pf

From newtons second law

6. Sep 4, 2008

LowlyPion

I understand what Conservation of momentum is thanks.

I was asking you what the terms were in the equation you wrote? What is m1 and u1 and ... etc.

7. Sep 4, 2008

ollieman

My text just says i can use either

m1u1 + m2u2 = m1v1 + m2v2

or

$$\sum$$ Pi = $$\sum$$ Pf

8. Sep 4, 2008

LowlyPion

Yes the first is the two body form of the second.

Now what is m1 and m2 ?
What is u1 and u2 and v1 and v2?

9. Sep 4, 2008

ollieman

m1 mass of the first object
m2 mass of the second object
u1 initial velocity of the first object
u2 initial velocity of the second object
v1 final velocity of the first object
v2 final velocity of the first object

Sorry i just thought it was how it worked, but it must be only how I'm taught

10. Sep 4, 2008

LowlyPion

There you go. Good.

Now look at your problem and start assigning values. (Remember since it is inelastic you will have both final velocities equal.)

11. Sep 4, 2008

ollieman

I couldn't get it out right :s that's why i posted it on here

12. Sep 4, 2008

LowlyPion

They give you the mass of the 2 wagons. What do you figure those are then in the equation?

Plug them in.

The velocity of one of the wagons is given. Plug that in.

Then solve for the final velocity.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook