95MH-2
Sr. No. 6
EXAMINATION OF MARINE ENGINEER OFFICER
Function: Marine Engineering at Management Level
MECHANICS AND HYDROMECHANICS
India (2003)
M.E.O. Class II
(Time allowed - 3hours)
Morning Paper
Total Marks 100
NB :
(1) Answer SIX Questions only.
(2) All Questions carry equal marks
(3) Neatness in handwriting and clarity in expression carries weightage
(4) Illustration of an Answer with clear sketches / diagrams carries weightage.
1.
A hand winch consists of a two-start square-thread worm on the driving shaft meshing with a gear
wheel of 84 teeth, the helix angle of the teeth being 15° and the coefficient of friction between the
square thread and teeth of the gear wheel is 0.105. The diameter of the lifting drum on the wheel
shaft is 350 mm, the diameter of the rope is 25 mm, and the effective radius of the handle on the
worm shaft is 250 mm. Find the effort required at the handle to lift a mass of 150 kg, taking the
efficiency of the thread and worm as the efficiency of the winch and neglecting other frictional
losses.
2.
A mild steel bar 50 mm diameter and 430 mm long is reduced in diameter to 40 mm along the
centre part of the bar for a length of 180 mm. When subjected to an axial pull the total elongation
is 0.5 mm. Taking E for steel as 210 GN/m2, calculate the tensile load, the resilience in each part
of the bar, and the total resilience.
3.
A casting of mass 50 kg is placed on a plane inclined at 30° to the horizontal. If the
coefficient of friction is 0.4, find the time taken for the casting to slide down the plane a distance
of 10 m without any external force being applied. Find also, the force required to give the casting
an acceleration of 2 m/s2 up the plane.
4.
A tube 5 m long, 13 mm outside diameter and 1.5 mm thick, is coiled into a helical spring of mean
coil diameter 150 mm. The spring is placed in a cylinder to oppose the motion of a piston in the
cylinder. The diameter of the piston is 200 mm and the effective pressure on the piston is 0.105
bar (= 0.105 x 105 N/m2). Calculate (i) the twisting moment applied to the spring, (ii) the
maximum stress in the spring, and (iii) the energy stored in the spring. The modulus of rigidity of
the spring material is 103 GN/m2 .
5.
The mean radius of a bend in the road is 100 m and that part of the road is banked to an angle of
10 degrees. Taking the coefficient of friction between tyres and ground as 0.65, calculate (a) the
speed in km/h at which a vehicle will be about to skid sideways, (b) if the coefficient of friction is
reduced to 0.3 due to wet conditions, what is now the critical speed?
6.
A tanker is steaming due south at 16 knots. At 12 noon a passenger ship is 7.5 nautical miles due
west of the tanker and steaming South East at 18 knots. At what time will the two ships be closest
together and what is then their distance apart.
7.
The total mass of a flywheel and shaft is 2.54 tonne, the radius of gyration is 686 mm and its
running at 150 rev/min. The torque required to overcome friction at the bearings is 27 Nm, Find
(i)
the kinetic energy stored in the wheel and shaft,
(ii)
the energy lost per revolution due to friction
(iii) the number of revolutions made in coming to rest when uncoupled from the driving
motor
(iv)
the time to come to rest
8.
A cantilever of hollow rectangular box section is constructed of steel of density 7.86 g/cm 3. Its
dimensions are : outside breadth 78mm , outside depth 104 mm, length 1.2 m, and it is 12 mm
thick through out. If the maximum stress is not to exceed 35 MN/m2 , calculate the maximum
concentrated load that can be carried at the free end of the beam.
9.
A circular opening, 3 m diameter, in the vertical side of a tank is closed by a disc of 3m diameter
which can rotate about a horizontal diameter. Calculate :
(i)
The force on the disc.
(ii)
The torque required to maintain the disc in equilibrium in the vertical position when the
head of water above the horizontal diameter is 4 m.
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