Find the final velocity of the railroad car.

[ScullyX51]

Homework Statement

A 1.00×104 railroad car is rolling at 4.00 when a 2000 load of gravel is suddenly dropped in. What is the car's speed just after the gravel is loaded?

Homework Equations

f=ma
pi=pf

The Attempt at a Solution

I am very confused with this problem, but this is what I have tried so far:
I drew a "before" picture of mass1: 2000kg, and mass2: 1.00*10^4kg. both in the y direction.
Then I drew an "after" picture of "m1+m2" moving in the x direction (m1+m2)Vf. and vf is given to be 4 m/s.
I don't know what to do from here, and I am also very confused because it seems as though it is not conservation of momentum in the collision in the y direction because of the force of gravity, and the normal force from the train. I would appreciate if someone could give me some hints on how to approach this problem.
Thank you. :)

 

[Doc Al]

I drew a "before" picture of mass1: 2000kg, and mass2: 1.00*10^4kg. both in the y direction.

What do you mean "in the y direction"?

Then I drew an "after" picture of "m1+m2" moving in the x direction (m1+m2)Vf.

This is good.

and vf is given to be 4 m/s.

No, 4 m/s is the initial velocity of the empty railroad car.

Hint: Just worry about the x-direction.

 

[asleight]

Homework Statement

A 1.00×104 railroad car is rolling at 4.00 when a 2000 load of gravel is suddenly dropped in. What is the car's speed just after the gravel is loaded?

Homework Equations

f=ma
pi=pf

The Attempt at a Solution

I am very confused with this problem, but this is what I have tried so far:
I drew a "before" picture of mass1: 2000kg, and mass2: 1.00*10^4kg. both in the y direction.
Then I drew an "after" picture of "m1+m2" moving in the x direction (m1+m2)Vf. and vf is given to be 4 m/s.
I don't know what to do from here, and I am also very confused because it seems as though it is not conservation of momentum in the collision in the y direction because of the force of gravity, and the normal force from the train. I would appreciate if someone could give me some hints on how to approach this problem.
Thank you. :)

Conservation of horizontal momentum is what you're after.