A person pushes on a doorknob with a force of 5.00 N. The direction of the force is at an angle of 20.0° from the perpendicular to the surface of the door. The doorknob is located 0.800 m from axis of the hinges of the door
The door begins to rotate with an angular acceleration of 2.00 rad/s2. What is the moment of inertia of the door about the hinges? A)
4.28 kg?m2
B)
7.52 kg?m2
C)
1.88 kg?m2
D)
0.684 kg?m2
E)
2.74 kg?m2
C
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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)
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Not only does the central engine of active galaxies and quasars require a black hole, but also ________ to provide the radiate energy
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A baseball pitcher is employing a ballistic pendulum to determine the speed of his fastball. A lump of clay is suspended from a cord 2.0 m long
When the pitcher throws his fastball aimed directly at the clay, the ball suddenly becomes embedded in the clay and the two swing up to a maximum height of 0.080 m. If the mass of the baseball is 0.21 kg, find the speed of the pitched ball.