Layers of 23-cm-thick meat slabs (k = 0.47 w/m·°c and α = 0.13*10-6 m2 /s) initially at a uniform temperature of 7°c are to be frozen by refrigerated air at -30°c flowing at a velocity of 1.4 m/s. the average heat transfer coefficient between the meat and the air is 20 w/m2 ·°c. assuming the size of the meat slabs to be large relative to their thickness, determine how long it will take for the center temperature of the slabs to drop to -18°c. also, determine the surface temperature of the meat slab at that time. (25 points)

Afoot bridge is made as a simple deck, 4 m long, with a cross section 2 m (wide) and 20 cm thick, and made of wood. the deck is supported at the two ends. the maximum load allowable on the bridge is 10 tons, provided it is uniformly distributed on the deck. to sense this load, a strain gauge is placed at the center of the bridge and its resistance is monitored. if the sensor has a nominal resistance of 350 s2 and a gauge factor of 3.6, what is the reading of the strain gauge at maximum load? the modulus of elasticity for the wood used in the construction is 10 gpa.