 
Summary: SUPPLEMENTARY HOMEWORK FOR WEEK 5
MATH2573H, SPRING 2012, UNIVERSITY OF MINNESOTA
GREG W. ANDERSON
Salt tank problem
A large tank initially contains 240 gallons of water and 35 pounds of salt. At
time t = 0 brine begins to flow into the tank at a rate of 4 gal/min. The brine
contains salt at a concentration of 4 pounds per gallon. Wellmixed solution is
allowed to drain from the tank at a rate of 7 gal/min. Find the amount of salt in
the tank at time t (until the tank runs dry).
Coroner's report
A body is discovered in a park at 3am in the morning. All through the evening
the temperature is a steady 45o
Fahrenheit. The temperature of the body is mea
sured at 3am and again at 4am just before moving the body to the morgue. The
temperatures are 80o
and 60o
Fahrenheit, respectively. Estimate the time of death
using Newton's law of heating/cooling. Start with the differential equation.
Logistic equation
Find the general solution of the differential equation
