Chapter 3: Q14E (page 113)
Chapter 3: Q14E (page 113)
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(a) Since the DE is autonomous, use the phase portrait concept of Section 2.1 to find the limiting value of as . Interpret the result.
(b) Solve the DE subject to . Sketch the graph of and verify your prediction in part (a).
Solve Problem 23 under the assumption that the solution is pumped out at a faster rate of . When is the tank empty?
Suppose that a glass tank has the shape of a cone with circular cross section as shown in Figure 3.2.10. As in part (a) of Problem 33, assume that corresponds to water filled to the top of the tank, a hole in the bottom is circular with radius in., , and . Use the differential equation in Problem 12 to find the height h(t) of the water.
(b) Can this water clock measure 12 time intervals of length equal to 1 hour? Explain using sound mathematics.
A heart pacemaker, shown in Figure 3.1.15, consists of a switch, a battery, a capacitor, and the heart as a resistor. When the switch Sis at P, the capacitor charges; when Sis atQ, the capacitor discharges, sending an electrical stimulus to the heart. In Problem 58 in Exercises 2.3 we saw that during this time the electrical stimulus is being applied to the heart, the voltageE across the heart satisfies the linearDE.
(a) Let us assume that over the time interval of length the switch S is at position P shown in Figure 3.1.15 and the capacitor is being charged. When the switch is moved to position Q at time the capacitor dis-charges, sending an impulse to the heart over the time interval of length . Thus over the initial charging/discharging interval the voltage to the heart is actually modelled by the piecewise-linear differential equation
By moving S between P and Q, the charging and discharging over time intervals of lengths and is
Repeated indenitely. Suppose , and and so on. Solve for for .
(b) Suppose for the sake of illustration that . Use a graphing utility to graph the solution for the IVP in part (a) for
Suppose an RC-series circuit has a variable resistor. If the resistance at time is defined by , where and are known positive constants, then the differential equation in (9) of Section 3.1 becomes
where C is a constant. If and , where and are constants, then show thatWhat do you think about this solution?
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