MAR. 5.]

THE NEW ZEALAND GAZETTE.

SPECIMEN SET OF PAPERS AS SET AT THE EXTRA FIRST-
CLASS EXAMINATION.

First Day: 9.30 a.m. to 12.15 p.m.

NOTE.--Candidates are not permitted to attempt more than three questions
in this paper.

1. A cylindrical air-receiver 3 ft. 6 in. diameter sustains a maximum
   working-pressure of 100 lb. per square inch. The longitudinal
   lap joint is single-riveted, the thickness of the shell ⅜ in., and
   the diameter and pitch of the rivets ¼ in. and 1¾ in. respectively. The tensile strength of the material is 30 tons per
   square inch, and the modulus of elasticity 30,000,000. Find--
   (a) the maximum stress in the shell due to bending action at
   the longitudinal joint; and (b) the total maximum stress in
   the shell.
   (45 marks.)

2. A triple-expansion steam-engine develops 3,000 indicated horse-
   power at 80 revolutions per minute, the work being equally
   distributed between the three cylinders. The diameter of the
   crank-shaft and the crank-pins is 14 in., the distance between
   the webs of each crank 14 in., and the length of the stroke
   4 ft. At half-stroke the pressure of the steam in the low-
   pressure cylinder, which is 72 in. diameter, is 10 lb. per square
   inch (gauge), and the pressure in the condenser 2 lb. per square
   inch absolute. Find, neglecting centrifugal forces and the
   obliquity of the connecting-rod, the stress in the low-pressure
   crank-pin due to bending moments when the crank has moved
   90 degrees from the top dead centre. (Note.--The low-
   pressure crank is aftermost.)
   (50 marks.)

3. A Diesel engine exhaust-valve spring having 24 coils is 26 in. long
   uncompressed, and 18·5 in. long in place when the valve is
   closed. The mean diameter of the spring is 4·5 in., and the
   diameter of the wire, which is of circular section, 0·6 in. If
   the total maximum load on the spring is 160 lb., find--(a) the
   lift of the valve, and (b) the maximum stress in the spring.
   (Note.--The candidate should show how formulae employed in
   solving this problem are derived.)
   (45 marks.)

4. What is the meaning of the term "creep strength" as applied to
   the materials of construction used by engineers? Describe
   the methods employed in determining the creep strength of a
   material, and explain the significance of this term in regard
   to modern engineering practice.
   (40 marks.)

First Day: 1.30 to 4 p.m.

NOTE.--Candidates are not permitted to attempt more than three questions
in this paper.

5. A vertical shipyard service boiler 5 ft. diameter sustains a maxi-
   mum working-pressure of 100 lb. per square inch. In conse-
   quence of its strength having been reduced by internal corrosion
   at the lower part of the shell, the boiler, which, when empty,
   weighs 2·75 tons, explodes when working at the maximum
   pressure. The portion of the shell above the bottom circum-
   ferential seam weighing 1·5 tons is severed from the lower
   part and projected into the air, the angle subtended by the
   line of its upward motion and the ground being 80 degrees.
   Assuming that the full steam-pressure acts on the shell for a
   period of one second from the time when the rupture occurs,
   and neglecting the frictional resistance of the atmosphere, find
   the distance between the two parts of the boiler when the
   upper part reaches the ground. (Note.--It is assumed that
   the lower part of the shell was not dislodged by the force of
   the explosion, and that the line of motion of the upper portion
   in ascending and descending was straight.)
   (50 marks.)

6. The twin cylinders of a locomotive are situated inside the frames,
   and the cranks are at right angles to one another. The
   rotating parts per cylinder, including two-thirds of the weight
   of the connecting-rod, are equivalent to a mass of 600 lb. con-
   centrated at the centre of the crank-pin, the distance between
   the centre-lines of the cylinders is 2 ft. 6 in., and the length
   of the stroke 2 ft. Find--(a) the weight to be placed in each
   driving-wheel at a radius of 3 ft. to balance the rotating parts,
   and (b) the position of each balance-weight relatively to the