What is the impulse of friction?

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    Friction Impulse
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Homework Help Overview

The discussion revolves around a momentum and impulse problem involving a block subjected to a force and kinetic friction. Participants are exploring how to incorporate friction into their calculations to determine velocity over time, particularly at specific intervals indicated on a graph.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between impulse and the area under the force-time graph, questioning how to account for friction in their equations. There are attempts to clarify the definitions of impulse and how it relates to the forces acting on the block. Some participants express confusion about calculating the average force at specific times and the implications of their findings.

Discussion Status

There is ongoing exploration of the problem, with some participants sharing their equations and results for specific time intervals. Guidance has been offered regarding the calculation of impulse and the need to consider friction as a constant force. However, multiple interpretations of the problem and its setup are being examined without a clear consensus on the correct approach.

Contextual Notes

Participants are working with a graph that represents forces over time, and there are mentions of specific time points (5 seconds and 8 seconds) where calculations are being made. The discussion includes references to the need for clarity in distinguishing between forces and impulses, as well as the assumptions regarding the constancy of kinetic friction.

Jason03
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I was working on a basic momentum/impulse problem where a block is pushed by a force P over a time T that is plotted on a graph...Kinetic Friction is given but how would I incorporate that into the equation to find the velocity?

I know the impulse is the area under the curve...

[tex]mv_{1} + F_{avg}\Delta{t} = mv_{}[/tex]
 
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What is the force of friction?
What is the impulse of friction?
How does that change your equation?
 
Actually I figured it out, pretty easy...I just over thought it as usual...
This equation allowed me to come up with the correct answer

[tex]mv_{1} + P-T(\Delta{t}) = mv_{2}[/tex]
 
Im having trouble coming up with velocity for Time at 8 seconds...I came up with the Velocity at 5 seconds easily using the equation above...

heres the graph for the problem...http://img91.imageshack.us/img91/6935/graphmp3.jpg


im trying to find the average Force at T = 8 seconds...but its not working
 
Last edited by a moderator:
Show what you did. To find the impulse of the applied force, find the area under the curve. What about the impulse of the friction force?
 
I used this equation to solve for time at 5 seconds...and it worked...

[tex]mv_{1} + P-T(\Delta{t}) = mv_{2}[/tex]


but I tried solving for time at 8 seconds... finding the area under the curve which is just a rectange and triangle...but the answer comes up incorrect

as far as area it should just be [tex](L * W) + (.5*b*h)[/tex]
 
Last edited:
Jason03 said:
I used this equation to solve for time at 5 seconds...and it worked...

[tex]mv_{1} + P-T(\Delta{t}) = mv_{2}[/tex]
That equation is not quite right. That second term (P) is a force, not an impulse. (It should be the area under that curve.)


but I tried solving for time at 8 seconds... finding the area under the curve which is just a rectange and triangle...but the answer comes up incorrect

as far as area it should just be [tex](L * W) + (.5*b*h)[/tex]
Looks fine to me. Show me the details. What did you get for the impulse due to the force P? The impulse due to the friction force T?
 


Don't forget that Impulse is NET force * time. So if you have the graph of the force of the engine vs. time, you need to subtract out kinetic friction, which is considered constant over the time.

If the MR2 that kept up well with the viper was a Spyder, that is I think 137 hp and not 115 hp.
 

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