# Conservation of momentum continous mass flow freight cart.

by BareFootKing
Tags: cart, conservation, continous, flow, freight, mass, momentum
 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
 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.
 Homework Sci Advisor HW Helper Thanks P: 8,876 your two links point to the same page, and I can't see anything there that matches either description.
P: 31

## Conservation of momentum continous mass flow freight cart.

Thank you I put up the wrong link. Here is the correct link:
 Homework Sci Advisor HW Helper Thanks P: 8,876 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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