A train that is momentarily at rest, Newton's Laws

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Homework Help Overview

The problem involves a train traveling up an incline and focuses on the dynamics of the last car after it breaks free and begins to coast without friction. The questions pertain to the time it takes for the car to come to rest and the distance it travels before doing so.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need to analyze the forces acting on the last car after it is released, particularly questioning how to determine the acceleration without knowing the mass or force involved. There is mention of using a free body diagram to visualize the problem.

Discussion Status

Some participants have identified that gravity is the primary force acting on the car after it is released, suggesting that the gravitational component along the incline can be calculated using sine. There appears to be a productive direction in understanding the forces involved.

Contextual Notes

Participants are working under the constraints of not having mass or specific force values, which complicates their ability to apply kinematic equations directly. The concept of "momentarily at rest" is also being examined in the context of the problem.

cloudage
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Homework Statement


A train is traveling up a 3.73 degrees incline at a speed of 3.25 m/s when the last car breaks free and begins to coast without friction.
a) How long does it take for the last car to come to rest momentarily?
b) How far did the last car travel before momentarily coming to rest?


Homework Equations





The Attempt at a Solution


I tried to draw the free body diagram, but since I have either mass or a force I don't know how to proceed. Momentarily at rest means that it's velocity is zero, but I don't know it's acceleration after the car has been released so I can't use the kinematics.
 
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cloudage said:

Homework Statement


A train is traveling up a 3.73 degrees incline at a speed of 3.25 m/s when the last car breaks free and begins to coast without friction.
a) How long does it take for the last car to come to rest momentarily?
b) How far did the last car travel before momentarily coming to rest?


Homework Equations





The Attempt at a Solution


I tried to draw the free body diagram, but since I have either mass or a force I don't know how to proceed. Momentarily at rest means that it's velocity is zero, but I don't know it's acceleration after the car has been released so I can't use the kinematics.
After the car is released, you should be able to find its acceleration. What net force acts on the car when it is released?
 
I got it, thank you very much! It would just be gravity acting on it, so I can find the component by using sine. Thanks!
 
cloudage said:
I got it, thank you very much! It would just be gravity acting on it, so I can find the component by using sine. Thanks!
Yes, and welcome to PF!
 

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