What forces are required to keep a car moving on a vertical loop?

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Homework Help Overview

The discussion revolves around a physics problem involving a cart moving through a vertical loop on a frictionless track. The original poster seeks to understand the relationship between the velocities at two points, A and X, where point A is higher than point X, which is at the top of the loop.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants question the clarity of the original poster's question regarding the velocity comparison between points A and X. There is a suggestion to specify the motion of the cart and the conditions of the problem. The role of energy conservation in the context of the problem is also discussed, alongside the need to consider forces acting on the cart at the top of the loop.

Discussion Status

The discussion is ongoing, with participants providing guidance on the importance of clarifying the problem and considering the forces involved in maintaining the cart's motion through the loop. There is an acknowledgment of the conservation of mechanical energy, but also a recognition that additional factors must be addressed to fully understand the dynamics at play.

Contextual Notes

Participants note that the original poster did not provide specific numerical values and that the problem requires a deeper exploration of forces acting on the cart, particularly at the top of the loop.

Larrytsai
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Point A
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- Point X (a Loop)
- - O
- -
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If this system is frictionless, and a cart is going down from point "A" to point "X" through the loop, What is the Velocity of Point "A" = to Point "X" ?
 
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I suspect you aren't going to get any takers on this problem until you clarify it (and show some of your own work). What exactly is the cart doing? Are you saying that it goes down a slope, around a (vertical) loop, and out to a final point? (I'm assuming the picture is to be viewed sideways.)

The question doesn't make much sense: what is "velocity of point A to point X" supposed to mean? The velocity is going to vary over this travel, so you are going to need to be more specific about what is needed...
 


dynamicsolo said:
I suspect you aren't going to get any takers on this problem until you clarify it (and show some of your own work). What exactly is the cart doing? Are you saying that it goes down a slope, around a (vertical) loop, and out to a final point? (I'm assuming the picture is to be viewed sideways.)

The question doesn't make much sense: what is "velocity of point A to point X" supposed to mean? The velocity is going to vary over this travel, so you are going to need to be more specific about what is needed...

ooo sry i thought i drew it with the keyboard, its just basically a rollercoaster picture with a loop. We weren't given any numbers, we just had to explain what is the velocity compared of point A to point x where point A is higher than point X, where point x is the top of the loop.


What my response was, Point A=Point X because the law of conservation of energy states energy is neither created or destroyed only transformed. Since the whole system is frictionless, then Energy is constant.
 


You are correct that mechanical energy (kinetic energy + potential energy) is conserved, but that isn't the only consideration in this problem. If you started the car from rest at exactly the same height as the top of the loop, the car would slow down as it approached the top, coming to a dead stop at the very top. Would it stay on the track if that happened?

You will need to look at the forces required to keep the car moving on the vertical loop, so that it can get beyond the top of the loop. (Remember, gravity is pulling straight down on it the whole time, including when it's inside the loop.)

Make a force diagram for the car at the moment it is at the top of the loop. What forces are acting on it there? What would have to be true about how these forces are related, in order for the car not to simply fall off the track at (or before, really) that point?
 

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