Air enters a 11-m-long section of a rectangular duct of cross section 15 cm × 20 cm made of commercial steel at 1 atm and 35°c at an average velocity of 5 m/s. disregarding the entrance effects, determine the fan power needed to overcome the pressure losses in this section of the duct. the properties of air at 1 atm and 35°c are rho = 1.145 kg/m3, μ = 1.895 × 10–5 kg/m·s, and ν = 1.655 × 10–5 m2/s. the roughness of commercial steel surfaces is ε = 0.45 m. the fan power needed to overcome the pressure losses is

Select the correct answer. anna will wear a black dress when she attends het cousin's wedding. which color(s) does the dress absorb? a. all colors b. no colors c. red and green d. white

Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold climates because it is light, fashionable, and a very effective thermal insulator. so it is no surprise that such clothing has largely replaced thickand heavy old-fashioned coats. (a) consider a jacket made of five layers of 0.1-mm-thick synthetic fabric (k = 0.13 w/m·°c) with 1.5-mm-thick air space (k = 0.026 w/m·°c) between the layers. assuming the inner surface temperature of the jacket to be 28°c and the surface area to be 1.25 m2, determine the rate of heat loss through the jacket when the temperature of the outdoors is 0°c and the heat transfer coefficient at the outer surface is 25 w/m2·°c. (b) what would your response be if the jacket is made of a single layer of 0.5-mm-thick synthetic fabric? what should be the thickness of a wool fabric (k = 0.035 w/m·°c) if the person is to achieve the same level of thermal comfort wearing a thick wool coat instead of a five-layer ski jacket?

Amoving electron has kinetic energy k1. after a net amount of work w has been done on it, the electron is moving one-quarter as fast in the opposite direction. (a) find w in terms of k1. (b) does your answer depend on the final direction of the electron's motion?