What is the intensity level of a sound with intensity 10-3 W/m2?
A) 96 dB
B) 30 dB
C) 79 dB
D) 90 dB
E) 60 dB
D
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A furnace wall is to be constructed of brick having standard dimensions 22.5 cm* 11 cm * 7.5 cm. Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 8700C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 10400C the hot side and 2000C on the cold side. If the maximum amount of heat transfer permissible is 950 W/m2 , determine the most economical arrangement using the available bricks.
GIVEN
Furnace wall made of 22.5 ? 11 ? 7.5 cm bricks of two types
Type 1 bricks Maximum useful temperature (T1,max) = 1040°C=1313 K
Thermal conductivity (k1) = 1.7 W/(m K)
Type 2 bricks Maximum useful temperature (T2,max) = 870°C= 1143 K
Thermal conductivity (k2) = 0.85 W/(m K)
Bricks cost the same
Wall hot side (Thot) = 1040°C=1313 K and cold side (Tcold) = 200°C=473 K
Maximum heat transfer permissible (qmax/A) = 950 W/m2
FIND
The most economical arrangement for the bricks
ASSUMPTIONS
One dimensional, steady state heat transfer conditions
Constant thermal conductivities
The contact resistance between the bricks is negligible
SKETCH
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Indicate whether the statement is true or false
A load is being lifted vertically upwards by means of two cables attached to it. The first cable exerts a force of 600 N at an angle of 35.0° to the left of the vertical. The second cable exerts a force of 1300 N
At what angle to the right of the vertical is the second cable pulling? A) 15.4° B) 16.2° C) 30.8° D) 67.8° E) 75.8°