Let A(t)= amount, in N of salt in tank A at time t. Then we have
dtdA=(rate of salt into tank A) − (rate of salt out of tank A)
dtdA=0−2008ASo we get the differential equation
AdA=−25dtIntegrate
A(t)=Ce−t/25Given A(0)=225. Then
A(t)=225e−t/25Let B(t)= amount, in N of salt in tank B at time t. Then we have
dtdB=(rate of salt into tank B) − (rate of salt out of tank B)
dtdB=2008(225e−t/25)−2008BdtdB+0.04B=e−0.04tdtdB+0.04B=0BdB=−0.04dtB=c1e−0.04tdtdB=dtdc1e−0.04t−0.04c1e−0.04tdtdc1e−0.04t−0.04c1e−0.04t+0.04c1e−0.04t=e−0.04tdtdc1=1c1=t+c2B(t)=(t+c2)e−0.04tGiven B(0)=0. Then
B(t)=te−0.04tHence
B(60)=60e−0.04(60)≈5.443 N
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