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Q9. (a) With aid of a simple sketch, show the normal positions of centre of gravity of a stable ship relative to keel, centre of buoyancy and meta centre. (6)

(b) A ship has 300 t of cargo in the hold, 24 m forward of the midships. The displacement of the vessel is 6000 t and its centre of gravity is 1.2 m forward of midships. Find the new position of the centre of gravity if this cargo is moved to an after hold, 40 m from midships. (10)

Q8. A bilge holding tank of 5 m length, 3 m width and 1.8 m depth has water of density 1.020 t/m3 upto a sounding of 1.3 m and oil of density 0.86 t/m3 is floating on top of water upto an ullage of 0.3 m. Calculate the mass of water and oil in the tank (16)

Q8. a) Explain clearly the meaning of the term "reserve buoyancy". (6)

b) The centre of gravity of a ship of 5000 tonne displacement is 6 m above the keel and 1.5 m forward of midships. Calculate the new position of the centre of gravity if 500 tonne of cargo are placed in the t’ween decks 10 m above the keel and 36 m aft of midships. (10)

Q7. A moving-coil instrument has a resistance of 10 Ω and requires a current of 15 mA to give full- scale deflection. Calculate the resistance value of the resistor necessary to enable it to be used to measure

a) currents up 25A

b) voltages up to 500V. (16)

Q5. A 4-pole lap wound DC shunt generator has an open e.m.f of 250V when the flux per pole is 0.08 Wb and the speed is 10 rev/sec. The speed of the generator is reduced to 10 per cent and the flux per pole is increased by 5% when the generator supplies a load of 100A. Determine the terminal voltage, if the armature resistance is 0.06 ohms and the new total field circuit resistance is 200 ohm. (16)

Q7. (a) Describe the function of the stern frame. (6)

(b) A ship displacing 10000 tonne and travelling at 16 knots has a fuel consumption of 41 tonne per day. Calculate the consumption per day if the displacement is increased to 13750 tonne and the speed is increased to 17 knots. Within this speed range, fuel consumption per day varies as (speed)^3.8 (10)

Q8. (a) What are the effects of adding mass to draught and trim of a ship? (6)

(b) The half ordinates of the waterplane area of a ship of 8200 t displacement, 90 m long are 0, 2.61, 3,68, 4.74, 5.84, 7.00, 7.30, 6.47, 5.35, 4.26, 3.16, 1.88 and o m respectively. It floats in sea water of 1.024 t/m3. Calculate the change in mean draught when moving into water of 1.005 t/m3 (10)

Q4. a) What design factor limits the maximum torque of a d.c. motor? (6)

(b) A shunt motor runs on no load at 700 r/min off a 440 V supply. The resistance of the shunt circuit is 240Ω. The following table gives the relationship between the flux and the shunt current:

Shunt current (A):      0.5   0.75   1.0   1.25   1.5   1.75   2.0

Flux per pole (mWb): 6.0   8.0   9.4   10.2   10.8   11.2   11.5

Calculate the additional resistance required in the shunt circuit to raise the no-load speed to 1000r/min (10)

Q5. a) Describe the effects of changes in speed, rotor current and torque as load is applied to an induction motor. How does the motor adjust its stator current with changes in mechanical load? (6)
b) A 20 KVA, 2000/220V, single-phase transformer has a primary resistance of 2.1 Ω and a secondary resistance of 0.026 Ω. The corresponding leakage reactance’s are 2.5 Ω and 0.03 Ω. Estimate the regulation at full load under power-factor conditions of:
(i) Unity

(ii) 0.5 (lagging)

(iii) 0.5 (Leading) (10)

Q4. a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6)
b) A transistor amplifier stage comprises a transistor of parameters hie = 800  hfe = 5O and hoe = 20µ S, and bias components and coupling capacitors of negligible effect. The input signal consists of an e.m.f. of 60 mV from a source of internal resistance 2.2 k , and the total load on the stage output is 4 k . Determine the current, voltage and power gains of the amplifier stage. (10)

Q4. A) With reference to voltage variation profiles caused by load changes imposed on alternating current generators when starting large motors online:

a) Sketch a voltage dip, showing an acceptable recovery time. (2)

b) State salient factors that cause the variation in part (a) (3)

c) Outline salient factors that assist recovery from the deviation shown in part (3)

B) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz System calculate:

a) The synchronous speed

b) The speed of rotor when the slip is 4 per cent.

c) The rotor frequency when the speed of the rotor is 600 r/min (8)

Q4. (a) Explain the significance of the root- mean- square value of an alternating current or voltage waveform. Define the form factor of such a wave form.  (6)

(b) A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor. (10)