(a) A horizontal steel I-beam of cross-sectional area 0.041 m2 is rigidly connected to two vertical steel girders. If the beam was installed when the temperature was 30°C, what stress is developed in the beam when the temperature drops to −30°C? (b) Is the ultimate strength of the steel exceeded? (c) What stress is developed if the beam is concrete and has a cross-sectional area of 0.13 m2? Will it fracture?

Solution 24PIntroductionIn this question, we have to apply the concept of relative density. Relative density is the ratioof density of a substance to that of water.SolutionStep 1:Given that, density of the wood block d wood = 700 kg/m 3 3We know that, density of freshwater d freshwater1000 kg/mTherefore, relative density of wood RD = 700/1000 RD = 0.7This means that 0.7 fraction or 70% of the wood will be submerged in freshwater.Height of the wood block = 10 cmIts height submerged in water is = 0.7 × 10 cm = 7 cm(a) Therefore, distance of the top of block to the water is = (10 7) cm = 3 cm