MAST10006 Calculus 2 Semester 2 Assessment, 2021
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Semester 2 Assessment, 2021
MAST10006 Calculus 2
In questions 1 and 2, you must state if you use standard limits, limit laws, continuity, l’Hˆopital’s rule, sandwich theorem, or convergence tests for series.
Question 1 (13 marks)
Let f (x) = ,0(t)an(x) log 3sin(x)、
(a) Use the definition of continuity to determine if the function f is continuous at x = 0.
Use the divergence test to determine if the series
n f ╱ 、
converges, or explain why the divergence test cannot be used.
Question2 (11 marks) Determine if each of the following series converge or diverge.
o
(a) n=1
^n
2(n!)
(b) o 4n + log(2 + )
n=1
Question 3 (5 marks)
(a) Use the exponential definition of the hyperbolic functions to prove the hyperbolic identity cosh(x - y) = cosh(x) cosh(y) - sinh(x) sinh(y), x, y e R.
Hence or otherwise, sketch the graph of
y = cosh(x) - tanh(2) sinh(x).
Question 4 (12 marks)
(a) Evaluate the integral
(b) Use the complex exponential to evaluate the integral e3北 cos 4x dx
Question 5 (7 marks) Consider the ODE
dy
(a) Find the general solution of the ODE.
(b) Sketch the family of solutions. Include solutions which pass through each of the following points:
i. (0, 0) ii. (1, 0) iii. (2, 0)
(c) Find the solution satisfying the initial condition y(3) = 0. What is the domain and range of the solution?
Question 6 (7 marks) Consider the ODE
dy y + x arctan(x) ^x2 - y2
=
dx x ,
y
x
= arctan(x) ^1 - u2 .
Find the general solution of the original ODE.
Question 7 (9 marks) Consider the ODE
dy
(a)
On the same set of axes, sketch the equilibrium solutions, and sketch the solution y(x) for each of the following initial conditions:
y(0) = 2; y(0) = 6; y(0) = 9
For which value(s) of y(0) is lim y(x) > 0?
北→o
Question 8 (9 marks) A 500L tank initially contains 100L of pure water. Beginning at time t = 0, water containing 0.5 g/L of pollutants flows into the tank at a rate of 2L/minute, and the well-stirred solution is drained out of the tank at a rate of 1L/minute.
The amount x(t) (in grams, g) of pollutant in the tank at time t minutes satisfies the ODE
dx x
dt 100 + t .
Find the concentration of pollutant in the tank at the moment the tank overflows.
Question 9 (10 marks) Consider the ODE
d2y dy
dt2 dt
where α e R and ω > 0 are constants.
(a) Let α = 6 and ω = 1. Find the general solution of the ODE.
For what value(s) of α and ω would a particular solution yp(t) of the inhomogeneous ODE have the form
yp(t) = at cos(ωt) + bt sin(ωt)
where a, b e R? Explain your reasoning.
Question 10 (7 marks) An object of mass 1kg is attached to a spring hanging vertically from a fixed support. The spring has spring constant k = 50 N m_1 . In equilibrium, the spring is stretched a distance s m. Assume that the gravitational constant is g = 10 m s_2 .
The system is subject to a damping force with damping constant β = 10 N s m_1 . In addition, a constant downward external force of f = 100 N is exerted on the object.
Let y(t) be the displacement in metres of the object below the system’s equilibrium position at time t seconds.
At t = 0 the object is released from rest, 0.2m below its equilibrium position.
(a) Use Newton’s 2nd law to show that the equation of motion for the system is y\\ + 10y + 50y\ = 100.
Include a diagram of the system at a time when the object is below its equilibrium position and moving up, with all forces shown and labelled.
(b) State the initial conditions, in terms of y and y\ .
(c) Let v(t) = y\ (t) be the velocity of the object. Differentiate the equation of motion to obtain a second-order ODE for v(t).
(d) Show that v\ (0) = 90.
Question 11 (13 marks) Consider the function f : R2 → R given by
f (x, y) = sech /^x2 + y2 、
and the surface S with equation X = f (x, y).
(a) Find the equation of the level curve of f at X = c.
(b) Sketch the level curve for each of the following values of c, or explain why it is not possible.
c = 1
(c) Find the equation of the cross section of S in the y-X plane, and sketch it.
(d) Sketch the surface S .
Prove that the direction of steepest increase of f at a point (x, y) e R2 / {(0, 0)} is in the direction of the vector v = (-x, -y). Interpret this geometrically.
Question 12 (7 marks) Let g : R2 → R be given by g(x, y) = (2y - y )e2_北2 .
(a) Find and classify the stationary points of g .
(b) Give an example of a point (x, y) e R2 where the gradient of g is non-zero and the direction
of steepest increase of g is parallel to the y-axis. Explain your reasoning, or explain why it is not possible to find such a point.
2023-05-31