Conservation of linear momentum

AI Thread Summary
The discussion centers on a physics problem involving a runaway railroad car with an initial mass of 14,000 kg moving at 4.00 m/s that collects 2000 kg of grain. Participants explore how to calculate the car's speed immediately after the grain drops and the impact of the grain leaking out at 10 kg/s on the car's momentum. The principle of conservation of linear momentum is emphasized, with questions raised about the relationship between initial and final momentum. Clarifications are sought regarding the effects of external forces on the system's horizontal momentum. The conversation highlights the complexities of determining the car's speed over a distance of 500 meters given the changing mass.
daivinhtran
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Homework Statement


A runaway 14,000 kg railroad car is rolling horizontally at 4.00 m/s toward a switchyard. As it passes by a grain elevator, 2000 of grain suddenly drops into the car. Suppose the there is a small vertical chute in the bottom of the car so that the grain leaks out at 10 kg/s. How long does it take the car to cover 500m


Homework Equations


Pi = Pf



The Attempt at a Solution


Picture attached
 

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daivinhtran said:

Homework Statement


A runaway 14,000 kg railroad car is rolling horizontally at 4.00 m/s toward a switchyard. As it passes by a grain elevator, 2000 of grain suddenly drops into the car. Suppose the there is a small vertical chute in the bottom of the car so that the grain leaks out at 10 kg/s. How long does it take the car to cover 500m


Homework Equations


Pi = Pf



The Attempt at a Solution


Picture attached
What is the initial horizontal momentum of the car and how does that relate to the horizontal momentum of the car + grain after the grain drops? Can you determine the speed of the car + grain after the drop? What effect does the vertical leak of grain have on the horizontal speed of the car?

AM
 
Andrew Mason said:
What is the initial horizontal momentum of the car and how does that relate to the horizontal momentum of the car + grain after the grain drops? Can you determine the speed of the car + grain after the drop? What effect does the vertical leak of grain have on the horizontal speed of the car?

AM

I already included those in my paper (attached).
However I can't determine the speed of the car + grain after drop unless I know the time.
 
daivinhtran said:
I already included those in my paper (attached).
However I can't determine the speed of the car + grain after drop unless I know the time.
Sure you can. How does the horizontal momentum before the collision compare to the horizontal momentum after the collision? (hint: are there any forces acting in the horizontal direction that are external to the car - grain system?).

AM
 
Andrew is asking what the speed is immediately after the drop, i.e. t = 0.
Separately, he asks what affect the grain leak has on the car thereafter.
 

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