Calculating Impulse and Force: Understanding the Concept Behind It

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Discussion Overview

The discussion centers around the concepts of impulse and force in the context of a homework problem involving a mass and applied forces. Participants explore the definitions and relationships between impulse, force, and their respective magnitudes and directions.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the wording of the homework question, particularly regarding the request for the force to be represented as a magnitude rather than including direction.
  • Another participant clarifies that the term "magnitude" implies a positive value, which may have contributed to the confusion.
  • Some participants suggest that the question should specify "magnitude of the average force" to avoid ambiguity.
  • There is a discussion about the distinction between impulse and impact, with some participants asserting that impulse refers to the change in momentum rather than the force itself.
  • One participant emphasizes that while impulse is negative, the force is presented as a positive magnitude, leading to further clarification on the relationship between the two concepts.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of impulse and force, but there is some disagreement regarding the interpretation of the homework question and the implications of representing force as a magnitude. The discussion remains somewhat unresolved as participants clarify their understanding without reaching a consensus on the wording issue.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the definitions of impulse and force, as well as the implications of directionality in the context of the homework question. The mathematical relationships presented are not fully resolved in terms of their implications for the problem at hand.

Ignitia
This is in relation to a homework question: But I don't need assistance on the question itself, but the concept behind it.

A mass of .4kg travels in the positive direction for 67m/s until a separate force is applied to M in the negative direction at 14m/s for .027 seconds. Impulse = 32.4 It then asks, "What is the average magnitude of the force?"

I'm more confused on the wording - as to what is it asking specifically? Why is the force being asked to be represented as a magnitude when it should have direction as well?

J = F Δt
F=J/Δt
F= -32.4N*s/.027s
F=-1200N

Yet the answer states 1200N. Impulse should be negative, since it's coming in from the negative direction, right?

What am I missing?
 
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It asks for the magnitude of the force, so therefore it would always be positive.

You also seem to be confusing impulse and impact; the former is the change in momentum not the force applied.
 
It probably should have been worded "magnitude of the average force"
 
person123 said:
You also seem to be confusing impulse and impact; the former is the change in momentum not the force applied.
I don't follow. I calculated the change of time in there: J=FΔt.

Dale said:
It probably should have been worded "magnitude of the average force"
That makes more sense. I realized I calculated directions into it when it didn't ask for it.
 
1200 Newtons is not the impulse; I'm not sure whether you thought it was or not.
 
person123 said:
1200 Newtons is not the impulse; I'm not sure whether you thought it was or not.
No no. Impulse was 32.4N*s in the negative direction. 1200N is the force.
 
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Oh, okay. It all seems good. :smile:
 
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Well, force consists of both a magnitude and a direction. You were already given the direction (the negative direction) so the only thing that's left to determine is the magnitude :).
 

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