Impulse: multiple choice question

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Homework Help Overview

The discussion revolves around a multiple-choice question related to impulse, specifically focusing on the calculation of force during a collision scenario. Participants are examining the discrepancies between their calculations and the provided correct answer.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are questioning the appropriateness of using certain equations for calculating time and acceleration in the context of a collision. There is a discussion about the assumptions regarding constant versus variable acceleration.

Discussion Status

The discussion is active, with participants providing guidance on the use of equations and clarifying assumptions. There is an acknowledgment of the need to assume constant acceleration for the problem to be solvable, and some participants express progress in their understanding.

Contextual Notes

There is a mention of the initial misunderstanding regarding the assumption of zero acceleration, which has been identified as a critical point in the discussion.

zanyzoya
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Hi all
Can anyone please help me with Q14 (attached) as you can see I am getting 167000N however the correct answer is 83000N
Many thanks
ZanyZoya
 

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Your estimate of the time for the collision (t = d/v) is inappropriate. This equation is used if the acceleration is zero. Here this is clearly not the case. What is is the average acceleration of a car that comes to rest over a distance of 0.30 m when it has initial speed 10 m/s?
 
Hmm we can’t use suvat equations as acceleration is not constant, we could use average acceleration =change in velocity/time but we don’t know time... hmm
 
zanyzoya said:
Hmm we can’t use suvat equations as acceleration is not constant ...
You have to assume that the acceleration is constant, otherwise you cannot solve the problem. What you cannot assume is that the acceleration is zero, which is what you did initially. So yes, use the SUVAT equations.
 
Thanks for your help kuruman, I think I’ve got it now.
 

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