
#1
Nov512, 04:32 PM

P: 31

1. The problem statement, all variables and given/known data
I am having difficulty understanding why in 2.1 Worked Example Coal Car on page 3 One can use the initial time as time = 0, but 2.2 Worked example on page 4 they start the initial time at an arbitrary time t. 2. Relevant equations 3. The attempt at a solution 



#2
Nov512, 04:36 PM

P: 31

because in the second example if you start with the initial time =0 then the initial momentum is zero because it is initially at rest and this simplifies the second example to a solutions similar to the first. But that is wrong.




#3
Nov612, 03:04 AM

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your two links point to the same page, and I can't see anything there that matches either description.




#4
Nov612, 09:57 AM

P: 31

Conservation of momentum continous mass flow freight cart.
Thank you I put up the wrong link. Here is the correct link:




#5
Nov612, 03:42 PM

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In each case they start at t=0. In 2.2 they also consider some arbitrary later time t and an interval δt from there. That is normal when deriving differential equations. In 2.1 they did not need to do that; they could solve the problem just by considering t=0 and t=t_{f} and applying conservation of momentum. Whether such an approach was available in 2.2 I've not tried to analyse.



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