Mass & Friction: Cart Question Answered

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Discussion Overview

The discussion revolves around the question of which of two carts, differing in mass but identical in size, reaches the bottom of a hill first when rolling down, while neglecting air resistance. Participants explore the effects of mass and friction on the carts' acceleration and timing.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that without friction, both carts would reach the bottom at the same time.
  • Others suggest that the heavier cart experiences greater friction, leading to the possibility that the lighter cart reaches the bottom first.
  • A participant notes that acceleration is inversely proportional to mass, implying that a greater mass results in lower acceleration, thus supporting the idea that the lighter cart reaches the ground first.
  • Another participant counters that this relationship holds only if the force acting on both carts is the same.
  • Some participants clarify that the acceleration is due to gravity alone, suggesting that both carts would have the same acceleration down the hill.
  • A later reply questions whether the problem is for schoolwork or general interest, indicating that additional context might be necessary to fully address the question.

Areas of Agreement / Disagreement

Participants express differing views on the role of mass and friction in determining which cart reaches the bottom first. There is no consensus on the outcome, as some believe the lighter cart will reach the bottom first while others argue that both carts will reach the bottom simultaneously due to equal gravitational acceleration.

Contextual Notes

The discussion does not specify the conditions under which friction is considered, nor does it clarify the nature of the forces acting on the carts beyond gravity. There are also unresolved assumptions regarding the problem's context, such as whether it is a schoolwork question or a general inquiry.

oobgular
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So suppose two carts roll down a hill. One is more massive than the other, but they both have the same size. Neglecting air resistance, which one reaches the bottom first?

Without friction, I think both reach the bottom at the same time. However my first thought was that the heavier car will have a greater friction force, the lighter one will reach the bottom first. However, I'm not sure if the mass cancels from all the friction terms. Any insight?
 
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oobgular said:
So suppose two carts roll down a hill. One is more massive than the other, but they both have the same size. Neglecting air resistance, which one reaches the bottom first?

Without friction, I think both reach the bottom at the same time. However my first thought was that the heavier car will have a greater friction force, the lighter one will reach the bottom first. However, I'm not sure if the mass cancels from all the friction terms. Any insight?
Why not write out the equations and find out for sure?
Another approach is dimensional analysis. Are you familiar with that?
 
Well, let's consider the acceleration, a
F=m.a
a=f/m
So,
a ∝ 1/m
This means greater the acceleration, the lower has to be the mass ( or vice versa)
So, for a greater mass acceleration will be lower
Thus,the lighter cart reaches the ground first for the same force.
 
Last edited:
shihab-kol said:
a ∝ 1/m
Only if F is the same for both.
 
haruspex said:
Only if F is the same for both.
Exactly
thanks
 
shihab-kol said:
Exactly
thanks
But it isn't.
 
haruspex said:
But it isn't.
But that is not specified by oobgular
 
shihab-kol said:
But that is not specified by oobgular
The question says they are rolling down a hill. It does not say they are being pushed down by some unspecified force. We can safely assume the acceleration is purely a result of gravity.
 
haruspex said:
The question says they are rolling down a hill. It does not say they are being pushed down by some unspecified force. We can safely assume the acceleration is purely a result of gravity.
Yes
Then the acceleration is equal for both.
 
  • #10
oobgular said:
So suppose two carts roll down a hill. One is more massive than the other, but they both have the same size. Neglecting air resistance, which one reaches the bottom first?

Without friction, I think both reach the bottom at the same time. However my first thought was that the heavier car will have a greater friction force, the lighter one will reach the bottom first. However, I'm not sure if the mass cancels from all the friction terms. Any insight?
@oobgular -- is this a question for schoolwork? Or just a general interest question?

If it's for schoolwork, I would expect that there would be more to the problem statement. Like, is just the body of the cart heavier, or the wheels, or both?

If it's for general interest, you probably need to give more thought to the various affects that more weight will have, in order to answer the question well. :smile:
 

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