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Revision Test 11: Torque, pressure in fluids, heat energy and transfer

When required take the density of water to be 1000 kg/m3 and gravitational acceleration as 9.81 m/s2.

1. Determine the force applied tangentially to a bar of a screw-jack at a radius of 60 cm, if the torque required is 750 N m. (4)

2. Calculate the torque developed by a motor whose spindle is rotating at 900 rev/min and developing a power of 4.20 kW. (5)

3. A motor connected to a shaft develops a torque of 8 kN m. Determine the number of revolutions made by the shaft if the work done is 7.2 MJ. (6)

4. Determine the angular acceleration of a shaft that has a moment of inertia of 32 kg m2 produced by an accelerating torque of 600 N m. (5)

5. An electric motor has an efficiency of 72% when running at 1400 rev/min. Determine the output torque when the power input is 2.50 kW. (6)

6. A circular piston exerts a pressure of 150 kPa on a fluid when the force applied to the piston is 0.5 kN. Calculate the diameter of the piston, correct to the nearest millimetre. (7)

7. A tank contains water to a depth of 500 mm. Determine the water pressure

(a) at a depth of 300 mm, (b) at the base of the tank. (6)

8. When the atmospheric pressure is 101 kPa, calculate the absolute pressure, to the nearest kiloPascal, at a point on a submarine which is 50 m below the sea water surface. Assume that the density of seawater is 1030 kg/m3. (5)

9. A body weighs 2.85 N in air and 2.35 N when completely immersed in water. Determine (a) the volume of the body, (b) the density of the body, (c) the relative density of the body. (9)

10. A submarine dives to a depth of 700 m. What is the gauge pressure on its surface if the density of seawater is 1020 kg/m3? (5)

11. A block of aluminium having a mass of 20 kg cools from a temperature of 250◦C to 80◦C. How much energy is lost by the aluminium? Assume the specific heat capacity of aluminium is 950 J/(kg ◦C). (5)

12. Calculate the heat energy required to convert completely 12 kg of water at 30◦C to superheated steam at 100◦C. Assume that the specific heat capacity of water is 4200 J/(kg ◦C) and the specific latent heat of vaporisation of water is 2260 kJ/(kg ◦C). (7)