Exam 1 Math 1360 September 27, 2017
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Exam 1 Math 1360 September 27, 2017
Work each problem on a separate page
Staple in upper LH corner when you hand in
Make plots BIG [1/2 page] and clear, Give clear and complete work.
Work is graded-not just final answers
Full justifications are needed for credit.
Use Calculators and scrap paper allowed
1. a. What are the 3 assumptions of Richardson’s model of arms races?
b. Write down his model and identify which assumption yields each term.
2. The system below has 2 equilibria.Pick one [NOT BOTH!], find the linearization at that equilibrium and classify the equilibrium.
x′ = 1 − x2 − y2 and y′ = x − y.
3. The number of worldwide facebook users N(t) for 3 years is listed below [in millions]
year 2009 2010 2011
#users 197 431 680 .
a. Assuming exponential growth, Calculate the doubling time for the num- ber of users. [There are more than 1 correct answer. Grade depends on work being complete and correct].
b. Assuming a logistic model instead, estimate the number of users when facebook saturates: limt→∞N(t). [Give clear and complete work as above.]
4. [Overshoot and collapse] Consider the simplified overshoot and collapse model for N(t)=population and R(t) = level of non-renewable resource.
A1: Logistic growth of population with carrying capacity proportional to resource level.
A2: Resource depletion rate is proportional to population.
a. Write down the 2 equation model from these assumptions.
b. Plot nullclines, trajectory directions and a few representative trajectories.
c. What is limt→∞N(t) and why?
2023-09-25