A 6.00-kg block is placed on a 30.0° incline and connected to another block on a 36.87° incline. Although the surfaces are frictionless the blocks do not move. What is the mass in kilograms of the block on the 36.87° incline?
?
?
A. 1.80
B. 3.00
C. 4.00
D. 5.00
E. 6.00
Answer: D
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Mercury is to be evaporated at 317°C in a furnace. The mercury flows through a 25.4 mm BWG No. 18 gauge 304 stainless-steel tube, that is placed in the center of the furnace. The furnace cross section, perpendicular to the tube axis, is a square 20 cm by 20 cm. The furnace is made of brick having an emissivity of 0.85, and its walls maintained uniformly at 977°C. If the convection heat transfer coefficient on the inside of the tube is 2.8 kW/(m2 K) and the emittance of the outer surface of the tube is 0.60, calculate the rate of heat transfer per meter of tube, neglecting convection within the furnace.
GIVEN
Mercury flow through a tube in the center of a furnace
Mercury temperature (Tm) = 317°C = 590 K
Tube specification: 25.4 mm BWG no 18 gauge stainless steel
Furnace cross section is 20 cm x 20 cm = 0.2 m x 0.2 m
Furnace emissivity (Tube specification: 25.4 mm BWG no 18 gauge stainless steel
Furnace wall temperature (T2) = 977°C = 1250 K
Tube interior heat transfer coefficient (hci) = 2800 W/(m2 K)
Tube exterior emissivity (?1) = 0.602) = 0.85
FIND
The rate of heat transfer per meter of tube
ASSUMPTIONS
Steady state
Convection within the furnace is negligible
SKETCH
the Stephan-Boltzmann constant
for 25.4 mm 18 BWG tubes
Inside diameter (Di) = 22.9 mm= 0.0229 m
Outside diameter (Do) = 25.4 mm = 0.0254 m
for type 304 stainless steel,the thermal conductivity (ks) = 14.4 W/(m K)