(a) For the U.S. census data, use the forward difference

Problem 27E Problem In Problems 23–27, assume that the rate of decay of a radioactive substance is proportional to the amount of the substance present. The half-life of a radioactive substance is the time it takes for one-half of the substance to disintegrate. The only undiscovered isotopes of the two unknown elements hohum and inertium (symbols Hh and It) are radioactive. Hohum decays into inertium with a decay constant of 2/yr, and inertium decays into the nonradioactive isotope of bunkum (symbol Bu) with a decay constant of 1/yr. An initial mass of 1 kg of hohum is put into a nonradiaoctive container, with no other source of hohum, inertium, or bunkum. How much of each of the three elements is in the container after t yr? (The decay constant is the constant of proportionality in the statement that the rate of loss of mass of the element at any time is proportional to the mass of the element at that time.)

1E Problem A brine solution of salt flows at a constant rate of 8 L/min into a large tank that initially held 100 L of brine solution in which was dissolved 0.5 kg of salt. The solution inside the tank is kept well stirred and flows out of the tank at the same rate. If the concentration of salt in the brine entering the tank is 0.05 kg/L, determine the mass of salt in the tank after t min. When will the concentration of salt in the tank reach 0.02 kg/L?

2E Problem A brine solution of salt flows at a constant rate of 6 L/min into a large tank that initially held 50 L of brine solution in which was dissolved 0.5 kg of salt. The solution inside the tank is kept well stirred and flows out of the tank at the same rate. If the concentration of salt in the brine entering the tank is 0.05 kg/L, determine the mass of salt in the tank after t min. When will the concentration of salt in the tank reach 0.03 kg/L?

Problem 5E Problem A swimming pool whose volume is 10,000 gal contains water that is 0.01% chlorine. Starting at t = 0, city water containing 0.001% chlorine is pumped into the pool at a rate of 5 gal/min. The pool water flows out at the same rate. What is the percentage of chlorine in the pool after 1 h? When will the pool water be 0.002% chlorine?

Problem 3E Problem A nitric acid solution flows at a constant rate of 6 L/min into a large tank that initially held 200 L of a 0.5% nitric acid solution. The solution inside the tank is kept well stirred and flows out of the tank at a rate of 8 L/min. If the solution entering the tank is 20% nitric acid, determine the volume of nitric acid in the tank after t min. When will the percentage of nitric acid in the tank reach 10%?

Problem 6E Problem The air in a small room 12 ft by 8 ft by 8 ft is 3% carbon monoxide. Starting at t = 0, fresh air containing no carbon monoxide is blown into the room at a rate of 100 ft3/min. If air in the room flows out through a vent at the same rate, when will the air in the room be 0.01% carbon monoxide?

4E Problem A brine solution of salt flows at a constant rate of 4 L/min into a large tank that initially held 100 L of pure water. The solution inside the tank is kept well stirred and flows out of the tank at a rate of 3 L/min. If the concentration of salt in the brine entering the tank is 0.2 kg/L, determine the mass of salt in the tank after t min. When will the concentration of salt in the tank reach 0.1 kg/L?

Problem 7E Problem Beginning at time t = 0, fresh water is pumped at the rate of 3 gal/min into a 60-gal tank initially filled with brine. The resulting less-and-less salty mixture overflows at the same rate into a second 60-gal tank that initially contained only pure water, and from there it eventually spills onto the ground. Assuming perfect mixing in both tanks, when will the water in the second tank taste saltiest? And exactly how salty will it then be, compared with the original brine?

Problem 8E Problem A tank initially contains S0 of salt dissolved in 200 gal of water, where S0 is some positive number. Starting at time t = 0, water containing 0.5 lb of salt per gallon enters the tank at a rate of 4 gal/min, and the well-stirred solution leaves the tank at the same rate. Letting c(t) be the concentration of salt in the tank at time t show that the limiting concentration- that is —-is 0.5 lb/gal.

Problem 10E Problem Use a sketch of the phase line (see Group Project C, Chapter 1) to argue that any solution to the mixing problem model approaches the equilibrium solution as x(t) = a/b as t approaches that is, a/b is a sink.

Use a sketch of the phase line (see Group Project C, Chapter 1) to argue that any solution to the logistic model \(\frac{d p}{d t}=(a-b p) p ;\ \ p\left(t_{0}\right)=p_{0}\), where ????, ????, and \(p_{0}\) are positive constants, approaches the equilibrium solution as \(p(t) \equiv a / b\) as ???? approaches \(+\infty\). Equation Transcription: Text Transcription: {dp}over{dt}=(a-bp)p; p(t_{0})=p_{0} p_{0} p(t) equiv a/b +infinity

Problem 13E Problem In Problem 9, suppose we have the additional information that the population of splake in 2004 was estimated to be 5000. Use a logistic model to estimate the population of splake in the year 2020. What is the predicted limiting population? [Hint: Use the formulas in Problem 12.]

Problem 9E Problem In 1990 the Department of Natural Resources released 1000 splake (a crossbreed of fish) into a lake. In 1997 the population of splake in the lake was estimated to be 3000. Using the Malthusian law for population growth, estimate the population of splake in the lake in the year 2020.

Problem 12E Problem For the logistic curve (15), assume pa: = p(ta) and pb: = p(tb) are given with tb = 2ta(ta > 0). Show that [Hint: Equate the expressions (21) for p0 at times ta and tb. Set and solve for . Insert into one of the earlier expressions and solve for p1.]

Problem 14E Problem In 1980 the population of alligators on the Kennedy Space Center grounds was estimated to be 1500. In 2006 the population had grown to an estimated 6000. Using the Malthusian law for population growth, estimate the alligator population on the Kennedy Space Center grounds in the year 2020.

In Problem 14, suppose we have the additional information that the population of alligators on the grounds of the Kennedy Space Center in 1993 was estimated to be 4100. Use a logistic model to estimate the population of alligators in the year 2020. What is the predicted limiting population? [Hint: Use the formulas in Problem 12.]

Show that for a differentiable function \(p(t)\), we have \(\lim _{h \rightarrow 0} \frac{p(t+h)-p(t-h)}{2 h}=p{\prime}(t)\), which is the basis of the centered difference approximation used in (20). Equation Transcription: Text Transcription: p(t) lim _{h rightarrow 0} {p(t+h)-p(t-h)}over{2h}=p’(t)

Problem 17E (a) For the U.S. census data, use the forward difference approximation to the derivative, that is, to recompute column 5 of Table 3.1. (b) Using the data from part (a), determine the constants A, p1 in the least-squares fit (c) With the values for A and p1 found in part (b), determine p0 by averaging formula (21) over the data. (d) Substitute A, p1, and p0 as determined above into the logistic formula (15) and calculate the populations predicted for each of the years listed in Table 3.1. (e) Compare this model with that of the centered difference-based model in column 6 of Table 3.1.

Problem 19E Problem 19. The initial mass of a certain species of fish is 7 million tons. The mass of fish, if left alone, would increase at a rate proportional to the mass, with a proportionality constant of 2/yr. However, commercial fishing removes fish mass at a constant rate of 15 million tons per year. When will all the fish be gone? If the fishing rate is changed so that the mass of fish remains constant, what should that rate be?

Problem 20E Problem 20. From theoretical considerations, it is known that light from a certain star should reach Earth with intensity I0. However, the path taken by the light from the star to Earth passes through a dust cloud, with absorption coefficient 0.1/light-year. The light reaching Earth has intensity ½ I0 . How thick is the dust cloud? (The rate of change of light intensity with respect to thickness is proportional to the intensity. One light-year is the distance traveled by light during 1 yr.)

Problem 21E Problem 21. A snowball melts in such a way that the rate of change in its volume is proportional to its surface area. If the snowball was initially 4 in. in diameter and after 30 min its diameter is 3 in., when will its diameter be 2 in.? Mathematically speaking, when will the snowball disappear?

Problem 22E Problem Suppose the snowball in Problem 21 melts so that the rate of change in its diameter is proportional to its surface area. Using the same given data, determine when its diameter will be 2 in. Mathematically speaking, when will the snowball disappear?

Problem 18E Problem Using the U.S. census data in Table 3.1 for 1900, 1920, and 1940 to determine parameters in the logistic equation model, what populations does the model predict for 2000 and 2010? Compare your answers with the census data for those years.

Problem 23E Problem In Problems 23–27, assume that the rate of decay of a radioactive substance is proportional to the amount of the substance present. The half-life of a radioactive substance is the time it takes for one-half of the substance to disintegrate. If initially there are 50 g of a radioactive substance and after 3 days there are only 10 g remaining, what percentage of the original amount remains after 4 days?

Problem 24E Problem In Problems 23–27, assume that the rate of decay of a radioactive substance is proportional to the amount of the substance present. The half-life of a radioactive substance is the time it takes for one-half of the substance to disintegrate. If initially there are 300 g of a radioactive substance and after 5 yr there are 200 g remaining, how much time must elapse before only 10 g remain?

Problem 25E Problem In Problems 23–27, assume that the rate of decay of a radioactive substance is proportional to the amount of the substance present. The half-life of a radioactive substance is the time it takes for one-half of the substance to disintegrate. Carbon dating is often used to determine the age of a fossil. For example, a humanoid skull was found in a cave in South Africa along with the remains of a campfire. Archaeologists believe the age of the skull to be the same age as the campfire. It is determined that only 2% of the original amount of carbon-14 remains in the burnt wood of the campfire. Estimate the age of the skull if the half-life of carbon-14 is about 5600 years.

Problem 26E Problem In Problems 23–27, assume that the rate of decay of a radioactive substance is proportional to the amount of the substance present. The half-life of a radioactive substance is the time it takes for one-half of the substance to disintegrate. To see how sensitive the technique of carbon dating of Problem 25 is, (a) Redo Problem 25 assuming the half-life of carbon-14 is 5550 yr. (b) Redo Problem 25 assuming 3% of the original mass remains. (c) If each of the figures in parts (a) and (b) represents a 1% error in measuring the two parameters of half-life and percent of mass remaining, to which parameter is the model more sensitive?