The ______________ is the remnant of a supernova explosion observed in A.D. 1054
Fill in the blank(s) with correct word
Crab Nebula
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In a metal manufacturing plant and its heat treatment process, a long, hexagonal copper extrusion (or rod) comes out of heat-treatment furnace at 400°C and is then quenched by immersing it in a 50°C air stream flowing perpendicular to its axis at 10 m/s as depicted in the figure. The surface of the copper has an emissivity of 0.9 due to oxidation in this process. The rod is 3 cm across opposing flat sides, and it has a cross-sectional area of 7.79 cm2, and a perimeter of 10.4 cm. Determine the time required for the center of the copper to cool to 100°C.
GIVEN
• A long hexagonal copper extrusion in an air stream flowing perpendicular to its axis
• Initial temperature (To) = 400°C
• Air temperature (T?) = 50°C
• Air velocity (V?) = 10 m/s
• Surface emissivity (?) = 0.9
• Distance across the flats (D) = 3 cm = 0.03 m
• Cross sectional area of the extrusion (Ac) = 7.79 cm2 = 7.79 × 10–4 m2
• Perimeter of the extrusion (P) = 10.4 cm = 0.104 m
FIND
• The time (t) required for the center of the copper to cool to 100°C
ASSUMPTIONS
• Variations of the copper properties with temperature are negligible
SKETCH
PROPERTIES AND CONSTANTS
Thermal conductivity (ka) = 0.0339 W/(m K) Kinematic viscosity (?) = 29.6 × 10–6 m2/s Prandtl number (Pr) = 0.71 For Appendix 2, Table 12, for copper
Thermal Conductivity (k) = 386 W/(m K) at 250°C Density (?) = 8933 kg/m3 at 20°C Specific heat (c) = 383 J/(kg K) at 20°C
What is quantum mechanics?
A) a branch of physics that applies on very small scales B) the idea that mechanics can be understood only if we first understand quantum C) the idea that quantitative methods are needed to understand physics D) a branch of physics that deals with the curvature of spacetime E) a branch of physics that deals with the properties of gases
All places on Earth would have high tides at the same instant if the
A) Moon did not revolve. B) Moon did not rotate. C) Sun did not revolve. D) Sun did not rotate. E) none of the above
A 2 500-kg car moving north collides with a 2 000-kg car moving west. After the collision, the cars stick together and move at an angle of 45° north of west at a speed of 8.0 m/s. What was the initial speed of the 2 500-kg car?
a. 20 m/s b. 10.2 m/s c. 14 m/s d. 9.3 m/s