PHYS1300 Maths 2 Semester Two 2020/2021
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PHYS130001
Maths 2
Semester Two 2020/2021
SECTION A
· You must answer all the questions from this section.
· This section is worth 20 marks.
· You are advised to spend 30 minutes on this section.
A1. (a) Insurance on a car decreases by 10% each year. If in the first year the insurance costs £1500, how many years (n) will it be before the insurance costs less than £150? [4]
(b) What is the total amount of insurance paid up to and including the year n? [3] (c) If the number of years tends to infinity, does the total amount paid converge?
Write down the reasoning behind your answer.
A2. The total differential of a function z = f(x, y) is given by
dz = dx + dy.
(a) What is meant by the total differential?
[3] [10 Marks]
[2]
(b) The moment of inertia of a uniform rod about one end is I = ML2 , where M is the mass and L is the length of the rod. If M = 400 ± 1 g and L = 20.0 ± 0.5 cm, calculate the uncertainty in I , and write the value for I in the form I ± dI with units and the correct number of significant figures. [8]
[10 Marks]
SECTION B
· You must answer all the questions from this section.
· This section is worth 45 marks.
· You are advised to spend 70 minutes on this section.
B1. A circular disc of radius 2 units is centred at the origin in the x - y plane. The areal density of the disc is given by σ(y2 + 1), where σ is a constant.
(a) Find the mass of the disc in terms of σ. Explain each step of your working. [10]
(b) How does the answer to part (a) change if the disc is centred at the point (0,1), instead of at the origin? [5]
[15 Marks]
B2. (a) Calculate Vf for the surface f (x, y, z) = x2 + y3 - 2z at the point (2,1,1). What is the meaning of Vf ? [5] (b) Calculate the rate of change of f (x, y, z) in the direction 2ˆ + at the point (2,1,1). [3]
(c) In what direction is the rate of change of f greatest at (2,1,1)? Justify your answer. Determine the rate of change in this direction at (2,1,1). [5]
(d) Find a unit vector that is normal to the surface at (0,0,0). Justify your method. [2]
[15 Marks]
B3. Two vector fields are described by A = z3 and B = 2y+ 2xzˆ+ 2z3 .
(a) Determine the divergence of each of the vector fields A and B. Taking each of the vector fields in turn, is there a source or sink of field lines at the point (1,1,1)? What does it mean if divA < divB? [7]
(b) The divergence theorem states S A.dS = V V.AdV, where S is the surface that encloses a volume V . Use the divergence theorem to evaluate the flux of A out of a sphere of radius R centred at the origin (Hint: it may be helpful to change coordinate system.) Deduce the flux of B out of the same sphere. [8]
[15 Marks]
2022-05-19