An 8-m-long, uninsulated square duct of cross section 0.2 m x 0.2 m and relative roughness 10^-3 passes through the attic space of a house. hot air enters the duct at 1 atm and 80°c at a volume flow rate of 0.15 m^3 /s. the duct surface is nearly isothermal at 60°c. determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. evaluate air properties at a bulk mean temperature of 80°c. is this a good assumption?

An engine, weighing 3000 n, is supported on a pedestal mount. it has been observed that the engine induces vibration into the surrounding area through its pedestal at the maximum operating speed. determine the stiffness of the dynamic vibration absorber spring in (n/m) that will reduce the vibration when mounted on the pedestal. the magnitude of the exciting force is 250 n, and the amplitude of motion of the auxiliary mass is to be limited to 2 mm note: in this question type-in right numbers, no decimals, no fractions, no unit. approximate to right number if needed