MATH2048 Mathematics for Engineering and the Environment Part II SEMESTER 1 EXAMINATION 2021/22
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SEMESTER 1 EXAMINATION 2021/22
MATH2048 Mathematics for Engineering and the Environment Part II
Section A: All students
A1. [Total for this question: 20 marks]
(a) [5 marks] Use the integral definition of the Fourier Transform F [f (t)] = F (ω) of a function f (t) to prove the property
F le-j atf (t)]= F (ω + a) .
(b) Consider the initial value problem:
(t) + 2α ˙(y)(t) = S(t) ; y(0) = K , ˙(y)(0) = 0 , (1)
where α > 0 and K are known constants, and the source term is:
S(t) = {0 cos t , t(t) π(π)
with A being a (known) constant.
(i) [8 marks] Express the source S(t) in terms of a Heaviside function and then use the indirect method of Laplace transforms to find that the Laplace transform solution ˜(y)(s) of this system is:
˜ K
Ae-πs
(s + 2α) (s2 + 1) (2)
(ii) [7 marks] Invert the Laplace transform (??) to find the solution y(t) of the original initial value problem (??).
A2. [Total for this question: 25 marks]
(a) Consider the wave equation
∂2u (3)
∂x2
with boundary conditions (` > 0)
u(0, t) = 0, At (4)
and initial conditions
u(x, 0) = δ(x - a) , A x 2 [0, `] , (5)
where 0 < a < ` is a constant and δ(z) is the Dirac delta function.
This system can be solved using the method of separation of variables whereby the most general solution is a series solution of the form
u(t, x) = Xn (x)Tn (t).
(i) [7 marks] Find Xn (x) and the associated eigenvalues λn (i.e. the separation constant), for positive integer n = 1, 2....
(ii) [6 marks] Find and solve the set of equations for Tn (t) (n = 1, 2...). (iii) [7 marks] Find the series solution u(t, x) that obeys not only the wave
equation (??) and the boundary conditions (??) but also the initial conditions (??).
(b) [5 marks] Consider the partial differential equation
= + + 2v) , (6)
where c and are constants.
Showing all your working, find the constant A so that the change of variable
v(t, x) = f (t) u(t, x) with f (t) = eAt
allows us to rewrite (??) as a standard wave equation for u(t, x): = .
Section B: All students except Civil Engineering
B. [Total for this question: 20 marks]
(a) [7 marks] An ellipse centered at the origin in the ①g-plane with semi-major axis a = 4 and semi-minor axis b = 3 can be parametrized as
YT(t) = 4 cost i + 3 sint j
where i,j, k are the three unit vectors of the Cartesian axes.
Find the work done by a particle subject to the force
F = (3x - 4g)i + (4x + 2g)j
when completing a single full turn around the ellipse, in an anticlockwise direction.
(b) [7 marks] Consider the closed surface S = ?V shown in Figure 1 which is
bounded by a paraboloidal-like lateral surface and by the “bottom” disk in the xg-plane. Assume that the volume V of the region that it encloses is V = π . Find the flux integral of the vector field F = (4x - 2xg)i - 2gj + 2gzk over the closed surface S = ?V.
Figure 1: Volume V bounded by the closed surface S = ?V of Question B.(b)
(c) [6 marks] Calculate the angle between the normal of the surface
x2 + 2g2 + z2 = 4 and the normal of the surface xgz + 3x2 = 4 , at the point (1, 1, 1).
Section C: Civil Engineering students only
C1. [Total for this question: 20 marks]
Where necessary report your answers to four decimal places.
(a) [5 marks] A bag contains 50 balls, 5 of which are black and the other 45 are
white. 5 balls are drawn randomly from the bag without replacement, that is, the ball(s) drawn will not be put back in the bag before the next ball is drawn. Find the probability that 3 of the 5 balls drawn are black.
(b) [5 marks] A bag contains 50 balls, 5 of which are black and the other 45 are
white. 5 balls are drawn randomly from the bag with replacement, that is, the ball drawn is inserted back in the bag before the next ball is drawn. Find the
probability that 3 of the 5 balls drawn are black.
(c) A plant produces water pumps. The life time of a pump, that is, how long a pump will last (measured in years), has an exponential distribution with mean β = 20 years, and the life times of the pumps vary independently of each other.
(i) [5 marks] Find the probability that a random selected pump will last at least 20 years.
(ii) [5 marks] A water supply system has 6 pumps arranged as in Figure 2
below, where the pumps operate independently.The system functions if water can flow from A to B. Find the probability that the water supply system functions for at least 20 years.
Figure 2: the water supply system of question C1.(c).(ii)
C2. [Total for this question: 15 marks]
Where necessary report your answers to two decimal places.
(a) [7 marks] We have two independent samples of 16 observations each, from
normal distributions with population means µ1 and µ2 , respectively, and the
same variance σ2. The sample means are 13.1 and 15.7 in sample 1 and sample 2, respectively. Moreover, the sample standard deviations are 0.89 and 0.82, respectively. Test, at the 5% significance level, the null hypothesis µ1 = µ2 against the alternative µ1 µ2 .
(b) In an investigation into the relationship between the strength y (modulus of
rupture, in N/mm2) and the temperature x (in degrees Celsius) of a particular type of steel girder at a manufacturing plant, a random sample of 24 steel girders is selected and tested, and the strength and temperature are observed for each girder. It is thought that y might be related to x through a quadratic regression model y = α + βx + γx2 + , and the following output was produced in
Minitab as part of the regression analysis of the observed sample:
Regression Equation
y = -1061 + 12.99 x - 0.0233 x^2
Coefficients
Term Coef SE Coef T-Value P-Value
Constant * 572 -1.86 0.078
x * 5.38 2.41 0.025
x^2 * 0.0127 -1.84 0.080
S = 2.653 R-sq = 98.67%
(i) [2 marks] What conclusion you can draw from
R-sq = 98.67%
(ii) [4 marks] Calculate a 95% confidence interval for the regression coefficient . Test the null hypothesis that is equal to zero at the 5% significance level.
(iii) [2 marks] From the result in (b)(ii), would you use the quadratic regression model? Give your reason.
2024-01-18