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Find the final velocity of the railroad car.

by ScullyX51
Tags: forces, momentum, velocity
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ScullyX51
#1
Nov9-08, 04:09 PM
P: 36
1. The problem statement, all variables and given/known data
A 1.00104 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?


2. Relevant equations
f=ma
pi=pf


3. 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. :)
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Doc Al
#2
Nov9-08, 04:26 PM
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P: 41,304
Quote Quote by ScullyX51 View Post
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
#3
Nov9-08, 04:36 PM
P: 154
Quote Quote by ScullyX51 View Post
1. The problem statement, all variables and given/known data
A 1.00104 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?


2. Relevant equations
f=ma
pi=pf


3. 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.


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