PGCL Written Exam Questions for Mechanical Engineers (2010)

1. Draw TOP and LEFT SIDE VIEW of the object shown.

2. Define isotropic materials and homogeneous materials, give an example of each.

3. Define Boundary layer. Draw a sketch showing different boundary-layer flow regimes on a flat plate.

4. Find the maximum torsional shear stress in a solid circular shaft of  diameter 10 mm, when the applied torque is 30N.m.

5. Water flows at 8 kg/s through a diffuser with A₁=7×10^-4 m² and A₂=4×10^-3 m². Determine the increase in static pressure between section 1 and section 2. Assume frictionless flow and water density 1000 kg/m³. 

6. An elastic bar of cross section A and length L is held fixed at both ends. The bar has modulus of elasticity E and coefficient of thermal expansion α. Derive the expression for axial force due to temperature increase of ΔT. (Assume no buckling of the bar).

7. For the plane stress shown in the stress element, draw the Mohr’s circle to find the maximum in-plane shearing stress and corresponding normal stress.

8. Construct shear and bending-moment diagrams showing peak values for the simply supported beam loaded with the forces shown in figure.

9. Draw the open cycle gas turbine in simple block diagram form and show the corresponding processes on a T-S plane.

10. What is cavitation? List any two problems caused by caviations in turbines.

11. Compute the pressure drop when water flows at 3 liter/s through a steel pipe with diameter 50 mm and 40 m length. Assume, density of water 1000 kg/m³ and friction factor f=0.02.

12. A composite wall of two 0.5 m thick layers has a temperature 150ºC on one face and 10ºC on the other face. Thermal conductivity of Layer-1 is k₁=0.05 W/m-K and Layer-2 is k₂=0.5 W/m-K. 

Consider face area A₁=A₂=2 m². What is the combined thermal resistance of the wall? Find the heat transfer per unit surface area.