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1
CHAPTER 1
1.1 You are given the following differential equation with the initial condition, v(t = 0) = 0,
c dv = g ? d v2 dt m
Multiply both sides by m/cd
m dv m = g ? v2 c d dt c d
Define a = mg / c d
m dv = a2 ? v2 c d dt
Integrate by separation of variables,
¡ò a 2 ? v 2 = ¡ò m dt
A table of integrals can be consulted to find that
dv
cd
¡òa
2
1 dx x = tanh ?1 2 a a ?x
Therefore, the integration yields
1 v c tanh ?1 = d t + C a a m
If v = 0 at t = 0, then because tanh?1(0) = 0, the constant of integration C = 0 and the solution is
1 v c tanh ?1 = d t a a m
This result can then be rearranged to yield
v=
? gc d ? gm t? tanh? ? m ? cd ? ?
1.2 This is a transient computation. For the period from ending June 1:
Balance = Previous Balance + Deposits ? Withdrawals
PROPRIETARY MATERIAL. ¨Ï The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any me¡¦(»ý·«)