Question { HCL, 43965 }

why I-sections are considered to be stronger one than any
other ?
how does a ship floats?

Answer

Yes 'I 'sections are having more moment of inertia( second moment of inertia),hence bending movement is more .That is why 'I' sections are more stronger than rectangular sections which are having equal area of cross section. Here important point is area of cross-section. If we take two beams of one I section and the other rectangular section of same height and same width , the rectangular section is stronger because the area of cross section is more but the weight(which increase cost) is also more,Hence it should be clear the 'I'sections are stronger compared to other sections which are having same height , width and area of material cross section. This is because of moment of inertia=b*h*h*h/12.

Although ships are made of materials that are much denser than water, the density of a ship itself is its total weight (including, cargo, bunkers, stores, crew, etc.) divided by the external volume of the hull. This means that the hull must have an external volume that is big enough to give the whole ship a density that is just less than that of the water in which it floats. Ships are therefore designed to achieve that. Much of the interior of a ship is air (compared with a bar of steel, which is solid), so the average density, taking into account the combination of the steel, other materials and the air, can become less than the average density of water.
That is why the ship floats in the see. this is nothing but buoyance principle i.e the weight of the water displaced by the ship should be more than the weight of the ship

Question { Infosys, 7425 }

why...? turbo charger used in DG....?

Answer

Every body thinks that super charger increase the efficiency of the engine which is a wrong concept.The super charge increase the power to weight ratio but not the efficiency. The turbo super charger pumps more air (oxygen) into the cylinder so that more fuel can be burnt in the cylinder which increase the power so the same engine can develop more power by using the turbo charge compared to with out super charge, hence power to weight ration increase but not the efficiency