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Conservation of momentum continous mass flow freight cart.

by BareFootKing
Tags: cart, conservation, continous, flow, freight, mass, momentum
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BareFootKing
#1
Nov5-12, 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
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BareFootKing
#2
Nov5-12, 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.
haruspex
#3
Nov6-12, 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.

BareFootKing
#4
Nov6-12, 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:
haruspex
#5
Nov6-12, 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=tf and applying conservation of momentum. Whether such an approach was available in 2.2 I've not tried to analyse.


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