Engineering, 04.10.2019 21:20 Arealbot
The roof of a house consists of a 15-cm-thick concrete slab (k 5 2 w/m·k) that is 15 m wide and 20 m long. the convection heat transfer coefficients on the inner and outer surfaces of the roof are 5 and 12 w/m2 ·k, respectively. on a clear winter night, the ambient air is reported to be at 10°c, while the night sky temperature is 100 k. the house and the interior surfaces of the wall are maintained at a constant temperature of 20°c. the emissivity of both surfaces of the concrete roof cen98187_ch03_p142-236.indd 212 14/02/14 4: 34 pm chapter 3 213 is 0.9. considering both radiation and convection heat transfers, determine the rate of heat transfer through the roof, and the inner surface temperature of the roof. if the house is heated by a furnace burning natural gas with an efficiency of 80 percent, and the price of natural gas is $1.20/therm (1 therm 5 105,500 kj of energy content), determine the money lost through the roof that night during a 14-h period
Answers: 3
Engineering, 04.07.2019 18:10
Aloaded platform of total mass 500 kg is supported by a dashpot and by a set of springs of effective stiffness 72 kn/m. it is observed that when the platform is depressed through a distance x = 12.5 cm below its equilibrium position and then released without any initial velocity; it reaches its equilibrium position in the shortest possible time without overshoot. find the position and velocity of the loaded platform 0.10 sec. after its release. if a further load of 400 kg is added to the platform, find, i) the frequency of damped vibrations, and i) the amplitude of vibration after 2 complete oscillations, given that the initial amplitude is 15 cm.
Answers: 1
Engineering, 04.07.2019 18:10
Aflywheel accelerates for 5 seconds at 2 rad/s2 from a speed of 20 rpm. determine the total number of revolutions of the flywheel during the period of its acceleration. a.5.65 b.8.43 c. 723 d.6.86
Answers: 2
Engineering, 04.07.2019 18:10
At 12 noon, the count in a bacteria culture was 400; at 4: 00 pm the count was 1200 let p(t) denote the bacteria cou population growth law. find: (a) an expression for the bacteria count at any time t (b) the bacteria count at 10 am. (c) the time required for the bacteria count to reach 1800.
Answers: 1
Engineering, 04.07.2019 18:10
Shafts are machine elements that are used to a) carry axial loads b) direct shear loads c) transmit power d) rotate at constant speed e) none of the above circular and square shafts subjected to the same torque under the same circum behave a) the same way b) almost the same way
Answers: 2
The roof of a house consists of a 15-cm-thick concrete slab (k 5 2 w/m·k) that is 15 m wide and 20 m...
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